messagesign 1.0.0

# messagesign

A rust library to sign requests to mehal services based on the [AWS S3V4 approach](https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html). 
 
The implementation is based on the [s3v4](https://github.com/uv-rust/s3v4) library. 

 This crate provides a `signature` function that can be used to sign a request to an mehal services.

 Both functions return an `Error` generated by the `error_chain` crate which can be 
 converted to a `String` or accessed through the `description` method or `display_chain` 
 and `backtrace` methods in case a full backtrace is needed.

 # Examples
 
 ## Signing a request
 ```rust
    let signature: s3v4::Signature = s3v4::signature(
        url,
        method,
        &access,
        &secret,
        &region,
        &"brog",
        machineid
        "UNSIGNED-PAYLOAD", //payload hash, or "UNSIGNED-PAYLOAD"
    ).map_err(|err| format!("Signature error: {}", err.display_chain()))?;
``` 
 
 ### Using the signature data to make a request 

 #### Hyper 
 ```rust
        let req = Request::builder()
        .method(Method::GET)
        .header("x-mhl-content-sha256", "UNSIGNED-PAYLOAD")
        .header("x-mhl-date", &signature.date_time)
        .header("x-mhl-mid", &machineid)
        .header("authorization", &signature.auth_header)
 ```
 #### Ureq
 ```rust
    let agent = AgentBuilder::new().build();
    let response = agent
        .put(&uri)
        .set("x-mhl-content-sha256", "UNSIGNED-PAYLOAD")
        .set("x-mhl-date", &signature.date_time)
        .set("x-mhl-mid", &machineid)
        .set("authorization", &signature.auth_header)
 ```