Make parsing more relaxed

[chen-hongzhi]

Add ability to allow the comma trailing in the last element of array
(or map); and now can parse a string that enclosed in single-quotes by
defining a macro.

[lamont-granquist]

This should probably get broken up into two different PRs that address the trailing commas and the quote-style. It'd also be really useful to not have the quote-style be a compile-time #define.

Also, some tests for this functionality would be good to show that it works correctly in the different modes of operation.

I'm very interested in the trailing commas option (and in general all the JSON5 extensions). Dunno if @lloyd is still active, however.

[sunsided]

So ... is this one still alive?

[anjohnson]

Check out my branch (PR #211) which goes much further and adds support for most of the JSON5 spec.