Major rewrite & update

[daviddesmet]

• [x] Applied Algorithm Lucidity. Closes #47
• [x] Improved protocol versioning.
• [x] Added support for protocols Version 3 & Version 4. Closes #49
• [x] Added support for PASERK (Platform-Agnostic Serialized Keys) extension. Closes #50
• [x] Enhanced token validation. Closes #3
• [x] Kept support for custom algorithms & protocols.
• [x] Major code refactor to promote the use of Fluent API.
• [x] Added official JSON-based Paseto test vectors. Closes #51
• [x] Update NaCl.Core library. Closes #30
• [x] Drop Paseto.Cryptography dependency.
• [x] Setup GitHub Actions