Consistent, language independent logic

[YaraslauZhylko]

My code changes to implement consistent, language independent logic described in Issue #44.

All original tests from http://jsonlogic.com still pass successfully.

And I've added my own set of tests called lanaguage-independent.json (with temporary modified .gitignore) to show how the modified logic works.

I can also change the code to only accept a strongly limited set of arguments (see comment nr. 3 in Issue #44).

And as I've mentioned, I can modify the Python port (json-logic-py) to make it follow all latest changes.

[YaraslauZhylko]

@jwadhams , is there a chance you could review and merge this pull request any time soon?