Improvements

[potocpav]

Added tests, CI, formatting, comments, made the code more robust, changed the encoders/decoder behavior ...

• A bug was fixed where the pointer execution was backwards - now it's correct.

!!! The new version is not backwards compatible

• Modules and function were renamed liberally
• ToJSON instance now produces plain format ("/foo/bar") instead of URI format ("#/foo/bar")
• FromJSON intance accepts both formats
• The parser now rejects invalid escape sequences (a bare ~, or ~2) - they used to be accepted as literal characters, so a stored pointer like #/a~b no longer loads.
• A reference token with a leading zero ("/a/01") is no longer treated as an array index, as per RFC 6901.
• atKey with a numeric token (atKey "0") now indexes into arrays, not just objects - a lookup that used to return Nothing can start resolving.