Add JSHint license to package.json
Merge pull request #968 from theoreticaLee/master

Add JSHint license to package.json
added A LOT of tests
renamed isMozOrESNext to isAfterESNext;
added isAfterES5;
refactored ESnext/Moz support to raise errors on future features;
fixed several parsing issues

Signed-off-by: Bernard `Guyzmo` Pratz <guyzmo+github@m0g.net>