Add support of HJSON

I would like to use this tool in a project of mine.  I am allowing users to supply YAML, JSON and HJSON as their data.  The idea is to use a mime type to identify how to parse the data.  HJSON is really new, but it is a smart idea.  JSON has become a ubiquitous method for configuring projects and HJSON makes it a little easier for humans to edit without the need to deal with whitespace.  This makes it easy to edit with any tool.