GitHub webhook message validator

This package currently contains a single utility function, which may be used to validate the package of a GitHub webhook request against a shared secret.

Note that if you get the signature from the X-Hub-Signature header, you'll need to convert it to bytes via hex. One way is to use the hex crate decodetoslice function.

Example

```rust use githubwebhookmessage_validator::validate;

let signature = &vec![ 115, 109, 127, 147, 66, 242, 167, 210, 57, 175, 165, 81, 58, 75, 178, 40, 62, 14, 21, 136 ]; let secret = b"some-secret"; let message = b"blah-blah-blah";

assert_eq!(validate(secret, signature, message), true);