Add tab completion

[Wilfred]

TAB works fine in when starting node from bash, so we should be able to do the same thing inside Emacs.

[redguardtoo]

Yes, patch welcomed.

Here is tech memo,
http://stackoverflow.com/questions/20396698/get-tab-completion-in-custom-comint-mode

[joshbax189]

Hey I'd like to work on this feature, are patches still welcome?

[redguardtoo]

sure

[joshbax189]

Ok I have a working version at https://github.com/joshbax189/js-comint/tree/feat/company-completion
However, due to the use of callbacks, I need to enable lexical binding in js-comint. I'd like to do that in a separate PR so as not to confuse things.