new modifier # for symbol elimination.

[kohlhase]

When I am annotating something, I often come into the following situation:

I have an annotation I want to make but I realize that the two choices are morally the same symbol, and (in this case) 0 should import 1. In this case, I would like to type 01# to be placed in an editor of my choice (probably via the $EDITIOR environment variable) with both of the files loaded so that I can remedy the situation before I go on annotating. In this case I would import the mv module from smglom/mv in mathtalk.en.tex and remove the \symdecl*{iff} there. This is short and painless and gets rid of an otherwise annoying quality issue then and there.

Of course in the example above, there might also be three or more files involved (or choice numbers larger than digits), so we need to generalize the interaction slightly.

This could build on #27, so that should be done first.

[kohlhase]

Ah, I see that this is a bad example above, since it is an artefact of #20, but the situation described above exists nonetheless