Rename JSON::json to avoid run time errors

Hi,

here's a new version of the JSON::json() change. With the old code every call to JSON::json would lead to ``Fatal error: Constructor JSON::json() cannot be static in <file> on line <line>`` during runtime. 

I renamed the method to have a nicer name which also translates what the code does and replace the one occurrence within the Xataface code. Creating another "compatibility wrapper" doesn't make sense in this case, because nobody would be able to use it.

Cheers