[MLton] Added completion to esml-mlb-mode

[Stephen Weeks]

> 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.  I wonder if
it would be useful to have MLton spit out all the valid annotations in
response to some command-line switch so that esml-mlb-annotations
could be generated automatically.  This would also enable one to use
the same esml-mlb-mode with different compilers without having to
change the emacs list code.