Macro for localeconv call.

[Casperinous]

During the compilation of your library for a native application in android the following error was produced: error: undefined reference to 'localeconv'. After googling, it came up to be a common error produced by the NDKs. A solution utilizing macros was proposed to another json-related library having the same issue. I forked your project and implement the proposed solution, resulting in a successful compilation of the code.
I can make a PR but i would like to know if you prefer another name for the macro, or in general a different solution.
Current name of the macro is NO_LOCALE_SUPPORT.

[FSMaxB]

Yes, please make a PR to the master branch. Call the macro ENABLE_LOCALES and, if you don't mind, also add a CMake option of the same name that defaults to on.

Also: Note that get_decimal_point should return '.', not '\0' if no locales are used.

[FSMaxB]

I will probably make a new minor release that also includes backports of #49 and #184 from develop.

[Casperinous]

Also, one question regarding the CONTRIBUTION.md:
I am a bit confused there, I dug up in the discussion and checked the code and it looks like 4 spaces per indentation.

[FSMaxB]

Yes, 4 Spaces. This is a bug. Interesting that nobody noticed this so far, including me.