Support for TEAL v4

[nullun]

There has been a few new keywords added to the TEAL language which are currently missing from this plugin.

[Adriano Di Luzio]

Thanks for reporting it, I'll take a look when I find some time. Alternatively, would you like to give it a shot with a PR? All modifications should go to the teal.vim file.

[Adriano Di Luzio]

Partially fixed by #2.