Stable and feature-complete INI plugin implementation.

This pull request adds in all the GM-specific ini functionality that the existing plugin infrastructure was missing. This meant a full rewrite of the plugin, which had several major issues. 

Note that this required changing "ini_write_real()" on Windows to take a float instead of an int. This behavior is consistent with GM:S. 

I am unable to test the plugin on Windows, as it conflicts with the built-in Windows (platform) ini functions.