doc: how to check data, magic hashes, and magic signatures

[coolaj86]

~/.cargo/git/checkouts/rust-dashcore-b01a88e2cb0da4a0/521a76b/dash/src/signer.rs:

// for Rust

/// sign and get the ECDSA signature
pub fn sign(data: &[u8], private_key: &[u8]) -> Result<[u8; 65], anyhow::Error> {
    let data_hash = double_sha(data);
    let maybe_magic_sig = sign_hash(&data_hash, private_key);
    let magic_sig = maybe_magic_sig.as_ref().unwrap();
    println!("simple sign key {}", hex::encode(&private_key));
    println!("simple sign data {}", hex::encode(&data));
    println!("simple sign hash {}", hex::encode(&data_hash));
    println!("simple sign sig {}", hex::encode(magic_sig));
    println!("");
    maybe_magic_sig
}

// for WASM

use wasm_bindgen::prelude::*;

#[wasm_bindgen]
extern "C" {
    // Multiple arguments too!
    #[wasm_bindgen(js_namespace = console, js_name = log)]
    fn js_log(a: &str, b: &str);
}

/// sign and get the ECDSA signature
pub fn sign(data: &[u8], private_key: &[u8]) -> Result<[u8; 65], anyhow::Error> {
    let data_hash = double_sha(data);
    let maybe_magic_sig = sign_hash(&data_hash, private_key);
    let magic_sig = maybe_magic_sig.as_ref().unwrap();
    js_log("simple sign key:", &hex::encode(&private_key));
    js_log("simple sign data {}", &hex::encode(&data));
    js_log("simple sign hash {}", &hex::encode(&data_hash));
    js_log("simple sign sig {}", &hex::encode(&magic_sig));
    js_log("", "");
    maybe_magic_sig
}

~/.cargo/git/checkouts/rust-dashcore-b01a88e2cb0da4a0/521a76b/dash/Cargo.toml:

[dependencies]
wasm-bindgen = { version = "=0.2.99" }