Remove PHP JWT Framework Dependency

[little-apps]

Proposal

Have Little JWT independent of the PHP JWT Framework.

Requirements

• Come up with code to generate own signature for the JWT.
• Come up with code to validate the signature inside a JWT.
• Potentially using the Adapter design pattern for the different signature algorithms.
• Encode and decode header or payload to base64url.
• Encode and decode header or payload to JSON (with un-escaped slashes and Unicode characters).