Remove the '!' abbreviation 

Now that ! is a direct alias for +Expand+, it is no longer necessary for it to have its own symbol in the algorithm grammar. ! is not an informative character, I would take a wild guess that no one would ever guess what it does from the symbol (well maybe the name Expand isn't too informative either), so I think it would be no great loss to get rid of that shortcut. 

There is some immediacy to this issue since removing this expansion fixes a bug wherein doing -compare with sigsets as the arguments, with an algorithm containing "!" would fail due to the direct string replacement used in Transform::make altering the string used to create the GalleryOutput transform in the update AlgorithmCore::enroll. The rest of the expansions done in Transform::make are recursive steps, rather than direct string replacements so they don't cause the same issue.