Initial work on JSON5.stringify

basic support all available
tests included
space argument partially implemented, but not tested, so currently disabled (throws exception on use)
replacer argument is not implemented (throws exception on use)
more work on stringify method

* added tests for spaces argument
* testing many more corner cases
* fixed lots of problems
Documentation and changelog
isNaN should be on Number, not Object.
Merge pull request #35 from aeisenberg/stringify

Initial work on the JSON5.stringify method.

All complete.  Fully tested and documented. Will raise issues for remaining work.