Actionscript 3 Syntax Highlight mode

Added actionscript 3 syntax highlighting mode based on the clike.js mode with slight modifications for things like reg ex. 

Wasn't sure about specifying keywords etc as part of the mime type spec, as people then have to be diligent about setting ""text/x-actionscript"" as the mode. However i guess this would make it possible to add an actionscript 2 implementation for any brave souls. 

Also unsure as to the need for the amendment to addon/edit/continuecomment.js