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>
updated automatic comma insertion support (cf #950)
added es3 config option and updated tests to match es3 ; 
made es5 the default and updated tests to remove es5 ;
added info message to tell about es5 being default ;
added functions to encapsulate management of current version state

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