Support recursive references in json schema

[torymur]

Closes #96

Implementing recursive references feature by walking the json shema and counting ins and outs with defined max recursion depth of 3. Defining recursion depth higher than that probably should not be done, since each +1 step on the depth blows up regex's size exponentially. For example, for simple referential json schema level 5 will produce regex size over 700K, which seems counterproductive and likely to introduce performance issues. It also breaks even regex sensible defaults with CompiledTooBig error.

Also, for this reason having more sophisticated ref counter (counting different entities with their own recursion depths) won't work in current json schema implementation.

TODO:

• port main json_schema tests to rust
• encapsulate private parsing logic under parser struct
• add recursive feature with defined default depth
• adapt errors from anyhow to thiserror, handle errors
• add more tests
• add basic documentation

[torymur]

This is ready for review of the recursive feature itself, which is relatively limited in code.

Refactoring and encapsulation changes, ported tests, errors and combined coverage check could be ignored in review.
Tests confirm that the main logic wasn't affected in any way with the exception of the addition of recursive feature.

The rest of the work defined above will be done in a follow up to speed up merging this PR.

[dpsimpson]

I've gone through the recursive parts and everything looks right to me except for a bounds check that i commented on.

[torymur]

Appreciate you taking a look here! @dpsimpson 🚀