Add OSLog support

MIGRATION_GUIDE.md

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+# PrettyLogger Migration Guide
+
+This guide shows how easy it is to migrate from the old print-based API to the new OSLog-based API while keeping the same function names.
+
+## Overview
+
+PrettyLogger now uses Apple's unified logging system (OSLog) instead of `print` statements, providing better performance, privacy controls, and integration with system tools. The best part? **You keep using the same function names!**
+
+## Quick Migration
+
+### What Changes
+- **Function signatures**: New parameters for `category` and `privacy`
+- **Parameter format**: String interpolation instead of variadic parameters
+- **Logging backend**: OSLog instead of print statements
+
+### What Stays the Same
+- **Function names**: `logInfo`, `logError`, `logWarning`, etc.
+- **Import statement**: `import PrettyLogger`
+- **Basic usage patterns**
+
+## Step-by-Step Migration
+
+### 1. Simple Messages (No Changes Needed!)
+
+```swift
+// Before and After - EXACTLY THE SAME!
+logInfo("User logged in successfully")
+logError("Network connection failed")
+logWarning("Low memory warning")
+logDebug("Processing user data")
+```
+
+### 2. Multiple Parameters → String Interpolation
+
+```swift
+// Before (deprecated)
+logInfo("User:", username, "logged in at:", timestamp)
+logError("Error code:", errorCode, "message:", error.localizedDescription)
+
+// After (recommended)
+logInfo("User: \(username) logged in at: \(timestamp)")
+logError("Error code: \(errorCode) message: \(error.localizedDescription)")
+```
+
+### 3. Add Categories for Better Organization (Optional)
+
+```swift
+// Before
+logInfo("API request completed")
+logError("Database connection failed")
+logDebug("Cache hit for key: user_123")
+
+// After (enhanced with categories)
+logInfo("API request completed", category: "Network")
+logError("Database connection failed", category: "Database")
+logDebug("Cache hit for key: user_123", category: "Cache")
+```
+
+### 4. Add Privacy Controls for Sensitive Data (Optional)
+
+```swift
+// Before
+logDebug("Auth token: abc123xyz")
+logInfo("User email: [email protected]")
+
+// After (with privacy)
+logDebug("Auth token: \(token)", category: "Auth", privacy: .private)
+logInfo("User email: \(email)", category: "Auth", privacy: .private)
+```
+
+## Real-World Example
+
+### Before (Old API)
+```swift
+class AuthManager {
+    func login(email: String, password: String) -> Bool {
+        logInfo("Starting login process")
+        logDebug("Email:", email, "Password length:", password.count)
+
+        if email.isEmpty {
+            logError("Login failed:", "Email is empty")
+            return false
+        }
+
+        // Simulate API call
+        logTrace("Making API call to:", "/auth/login")
+
+        // Success
+        logInfo("Login successful for user:", email)
+        return true
+    }
+}
+```
+
+### After (New API)
+```swift
+class AuthManager {
+    func login(email: String, password: String) -> Bool {
+        logInfo("Starting login process", category: "Auth")
+        logDebug("Email: \(email) Password length: \(password.count)", 
+                category: "Auth", privacy: .private)
+
+        if email.isEmpty {
+            logError("Login failed: Email is empty", category: "Auth")
+            return false
+        }
+
+        // Simulate API call
+        logTrace("Making API call to: /auth/login", category: "Network")
+
+        // Success
+        logInfo("Login successful for user: \(email)", 
+               category: "Auth", privacy: .private)
+        return true
+    }
+}
+```
+
+## Migration Strategies
+
+### Strategy 1: Minimal Changes (Easiest)
+1. Replace variadic parameters with string interpolation
+2. Remove any `separator` and `terminator` parameters
+3. Done! Your logs now use OSLog
+
+### Strategy 2: Gradual Enhancement (Recommended)
+1. Start with minimal changes (Strategy 1)
+2. Gradually add categories to group related logs
+3. Add privacy controls for sensitive data
+4. Test with Console.app and Instruments
+
+### Strategy 3: Complete Modernization
+1. Apply minimal changes
+2. Define category constants
+3. Add comprehensive privacy controls
+4. Update log messages for better structure
+5. Add performance monitoring
+
+## Category Best Practices
+
+### Define Constants
+```swift
+extension String {
+    static let auth = "Authentication"
+    static let network = "Network"
+    static let database = "Database"
+    static let ui = "UserInterface"
+    static let cache = "Cache"
+}
+
+// Usage
+logError("Connection timeout", category: .network)
+logInfo("User authenticated", category: .auth)
+```
+
+### Hierarchical Categories
+```swift
+// Use dot notation for subcategories
+logDebug("Cache miss", category: "Cache.User")
+logInfo("Database query", category: "Database.Read")
+logError("Network timeout", category: "Network.API")
+```
+
+## Privacy Guidelines
+
+| Data Type | Recommended Privacy | Example |
+|-----------|-------------------|---------|
+| User IDs | `.auto` | `logInfo("User \(userID) logged in", privacy: .auto)` |
+| Email addresses | `.private` | `logDebug("Email: \(email)", privacy: .private)` |
+| Passwords/Tokens | `.private` | `logTrace("Token refreshed", privacy: .private)` |
+| App version | `.public` | `logInfo("App version: \(version)", privacy: .public)` |
+| Error messages | `.auto` | `logError("Network error: \(error)", privacy: .auto)` |
+
+## Testing Your Migration
+
+### 1. Compile and Run
+```bash
+# Make sure everything compiles
+swift build
+
+# Run your tests
+swift test
+```
+
+### 2. Check Console.app
+1. Open Console.app on macOS
+2. Filter by your app's bundle identifier
+3. Verify logs appear with proper categories
+4. Test privacy settings
+
+### 3. Use Command Line Tools
+```bash
+# Show logs from your app
+log show --predicate 'subsystem == "com.yourapp.bundleid"' --last 1h
+
+# Filter by category
+log show --predicate 'category == "Network"' --last 30m
+```
+
+## Common Issues and Solutions
+
+### Issue: Too Many Parameters
+```swift
+// Problem: Old habit of many parameters
+logInfo("User:", user.id, "action:", action, "result:", result, "time:", time)
+
+// Solution: Use string interpolation
+logInfo("User: \(user.id) action: \(action) result: \(result) time: \(time)")
+```
+
+### Issue: Missing Privacy Controls
+```swift
+// Problem: Sensitive data exposed
+logDebug("Processing payment for card: \(cardNumber)")
+
+// Solution: Mark as private
+logDebug("Processing payment for card: \(cardNumber)", 
+        category: "Payment", privacy: .private)
+```
+
+### Issue: No Categories
+```swift
+// Problem: All logs mixed together
+logError("Database connection failed")
+logError("Network request timeout")
+
+// Solution: Use categories
+logError("Database connection failed", category: "Database")
+logError("Network request timeout", category: "Network")
+```
+
+## Benefits After Migration
+
+✅ **Better Performance**: OSLog is faster and more efficient than print  
+✅ **Privacy Controls**: Automatic handling of sensitive data  
+✅ **System Integration**: Works with Console.app, Instruments, and log command  
+✅ **Structured Logging**: Categories help organize and filter logs  
+✅ **Production Ready**: Proper log levels for release builds  
+✅ **Same Function Names**: No need to learn new API  
+
+## Need Help?
+
+- Check `USAGE_EXAMPLES.md` for comprehensive examples
+- Use Console.app to verify your logs are working
+- Test privacy settings in release builds
+- Consider gradual migration for large codebases
+
+The migration is designed to be as smooth as possible while providing modern logging capabilities!