feature: add yaml set Package (#17)

The root level `package` key describes the package name.

Default is the directory name is not enough because it may contain a command
(package main). Find the first non-test file to get the real package name.

README.md

@@ -4,6 +4,7 @@ Easy, fast and type-safe dependency injection for Go.
 
   * [Installation](#installation)
   * [Building the Container](#building-the-container)
+  * [Configuring Package](#configuring-package)
   * [Configuring Services](#configuring-services)
     + [arguments](#arguments)
     + [error](#error)
@@ -54,6 +55,10 @@ services:
 
 It will generate a file called `dingo.go`. This must be committed with your
 code.
+## Configuring Package
+The root level `package` key describes the package name.
+
+Default is the directory name is not enough because it may contain a command (package main). Find the first non-test file to get the real package name.
 
 ## Configuring Services
 

dingotest/dingo.yml

@@ -1,3 +1,4 @@
+package: dingotest
 services:
   SendEmail:
     type: '*SendEmail'

file.go

@@ -13,6 +13,7 @@ import (
 )
 
 type File struct {
+	Package  string
 	Services Services
 	fset     *token.FileSet
 	file     *ast.File

main.go

@@ -32,7 +32,12 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
-	packageName := file.getPackageName(dingoYMLPath)
+
+	packageName := file.Package
+	if packageName == "" {
+		packageName = file.getPackageName(dingoYMLPath)
+	}
+
 	file, err = GenerateContainer(file, packageName, outputFile)
 	if err != nil {
 		log.Fatalln(err)