compare mathematical letter symbols for ForTheWin

Reintroduce an even more elaborate overview of letterlike scripts, dismissed
in commit 26e8aa257e (2015-09-12) [drop mathematical ABC symbols line].
While it remains as ill-advised for spelling out words, unfortunately it is
widely used that way nowadays (at least in Twitter user names).

Regardless, style should be consistent (especially considering characters
have been introduced in different versions) and distinct (as it's intended
for unique variables), so a comparison makes sense in any case.
Just put it after proper language scripts.