Switch _ResultIterator to using _Parser

[spbnick]

This is an attempt to reuse the _Parser for feeding programs with input data, which enables eventual processing of JSON streams with JQ programs.

Might not be the ideal approach, tell me what you think!

Please see more explanations in individual commit messages.

Based on and requires #51.

[spbnick]

Ah, one undesirable side-effect of this is that we now throw jq.JSONParseError instead of ValueError as some programs might expect. We can forgo the whole idea of a dedicated exception, of course, but I would personally prefer a line in release notes warning about that instead :)

[spbnick]

Added a commit fixing parsing of RS-separated streams (RFC 7464)

[spbnick]

Closing this outdated PR for another attempt.