Replaced JsonParser with a faster one

Replaces the existing JsonParser with a new, faster, one. 
- Hand-crafted instead of using the scala parser combinators. 
- It is 13 to 18 times faster, depending on the size of the document. 
- The parser is a drop-in replacement for the old one. 
- None of the existing tests were modified.

Why?

While doing some performance tests with retrieving data from Elastic Search, it turned out that 1/3 of the time was spent on the the actual query, including the round-trip to the ES server, and 2/3 of the time was spent on parsing strings to JSON. With this new parser, my queries became 3 times faster.