Fix #93 ($ref to local definition not working)

See also #110. This pull request is based @stoiev's branch. First, thanks for his great work!
(I skipped fc947a6c949af5302d81e8b3b409d5ead76bc0ca commit. Because it is not related with this problem and it contains some problems; composer.lock should not be ignored (see http://blog.naderman.de/2014/02/17/replace-conflict-forks-explained/) and netbeans project directories  should be ignored in $HOME/.gitignore)

And I've referenced some implementation of brandur/json_schema (it is Ruby JSON Schema validation library). I really appreciate to the library.

My fix resolves some problems of #110; e.g. the #110 implementation only resolves the top level of $ref but my implementation resolves any level of a path.

But, however, it doesn't pass json/tests/draft4/ref.json yet. We should effort resolve this problem too, but the inline dereferencing problem is needed to fix ASAP.