[MLton] Added completion to esml-mlb-mode

[Vesa Karvonen]

> Now, mlton -expert true -show-anns true displays:
> 
>   allowConstant {false|true}
>   allowFFI {false|true}
>   allowOverload {false|true}
>   allowPrim {false|true}
>   allowRebindEquals {false|true}
>   deadCode {false|true}
>   ffiStr {<longstrid>}
>   forceUsed
>   nonexhaustiveExnMatch {default|ignore}
>   nonexhaustiveMatch {warn|ignore|error}
>   redundantMatch {warn|ignore|error}
>   sequenceNonUnit {ignore|error|warn}
>   warnUnused {false|true}
> 
> Hopefully this doesn't cause too much problem for Vesa's (or other
> future) readers.  If it does, I'm willing to go with a more consistent
> format.

Nothing that a few regexps couldn't handle. I've updated esml-mlb-mode to
support the above format.

> > With regards to forceUsed, remember that it does not mean to mark every
> > identifier encountered in the body of the annotation as used; instead, it
> > means to mark as used all identifiers in scope at the end of the
> > annotation as used.
[...]
> Fair enough.  Although I don't find it difficult to read a forceUsed
> toggle as saying either "do" or "do not" mark everthing in scope at
> the end of the annotation as used.

After reading Matthew's note, I think that it is better to make it
syntactically apparent that the semantics of forceUsed is special.

-Vesa Karvonen