Added configurable submitKeys

[mirbuf]

Instead of default Enter key, any number of keys can be configured via optional submitKeys: [] array.
Defaults to Comma, Tab and Enter keys.

[LeaVerou]

Thank you for working on this! I like the flexibility of being able to specify your own keys, that is very on par with Awesomplete's design principles.
However, I still think Enter should be the default. Tab can interfere with tabbing through form controls, and comma could interfere when your actual options contain commas.

[AetherUnbound]

This seems like a great feature, but I agree that having it as default might be problematic. Perhaps it might be made more configurable, i.e. submitKeys initially only contains the enter key but there might also be a method to add one's own preferred default keys.
For instance, we hope to use awesomplete for entering directories. Tabs would be great for that, but perhaps not commas.

[mirbuf]

I added submitKeys defaulted that way as a PoC. I agree that could be left just Enter, or Enter + Tab as default keys. And a method to set the new option would be a nice addition. I'll eventually add it, later.

[mirbuf]

LeaVerou, I set default submitKeys to [ Enter ].
I also added a method to set user own submitKeys. You can:

setSubmitKeys( KEYCODE )
setSubmitKeys( [ KEYCODE1, ... , KEYCODEn ] )
setSubmitKeys( 'aeiou' ) // this will set 'A', 'E', 'I', 'O', 'U' keys keycodes

Let me know if this may be a more useful addition.

[LeaVerou]

Why do we need a function (and such a long one at that)? People can modify the submitKeys array, no?