[MLton] Added completion to esml-mlb-mode

[Vesa Karvonen]

Quoting Stephen Weeks <sweeks@sweeks.com>:
> > I have added context sensitive completion for annotations, paths and
> > path variables to esml-mlb-mode.
> 
> I just got a chance to play around with this.  Very nice.

Thanks. I plan to add completion of keywords. It would also be nice to have
completion of signature, structure, and functor identifiers, but it seems
considerably more difficult to do both properly and efficiently (scanning
through all the source files could take a lot of time and without a proper
parser it would probably be easy to misclassify identifiers).

> I wonder if it would be useful to have MLton spit out all the valid
> annotations in response to some command-line switch

I think that this would make sense as a form of self-documentation, independent
of esml-mlb-mode, similar to MLton spitting out the command line options upon
encountering an unrecognized option.

-Vesa Karvonen