Lots of Ruby libraries utilize JSON parsing in some form, and everyone
has their favorite JSON library. In order to best support multiple JSON
parsers and libraries, multi_json is a general-purpose swappable JSON
backend library.

MultiJSON tries to have intelligent defaulting. That is, if you have any
of the supported engines already loaded, it will utilize them before
attempting to load any. When loading, libraries are ordered by speed.
First Yajl-Ruby, then the JSON gem, then JSON pure. If no JSON library
is available, MultiJSON falls back to a bundled version of OkJson.
