Improve scheduler performance by reducing calling C code(NIF)

Although jsonx is faster than jsx for encoding/decoding json,
it calls C code through what's called a NIF. This may be fast,
but is blocking, messes the erlang scheduler (overheard on #erlang)

Hence the following changes:
- Use jsx instead of jsonx NIF
Merge branch 'master' of github.com:bosky101/kafboy