Initial support for Haxe 3, plus a few small changes, packaging for Haxelib

Hey Tom!

Thanks for the library.  I did a little bit of work to get it Haxe 3 (and Haxelib) ready, plus a tiny change or two I noticed.

I have only used the minimum required for my job, but so far so good :)

To upload this to haxelib:

    # First, edit haxelib.json to include your haxelib username in the contributors
    ./bundle.sh
    haxelib submit ckeditor-externs.zip

If you would like me to push to haxelib let me know