General TTX utility

So File::TTX may be slipping ever closer to irrelevance, but I'm still using it for a number of things. The only problem is, it's a pain always having to write a special-purpose Perl script just to change, say, the source language of a TTX.

Obviously, a command-line program would be the first step towards usability. (And way easier than a GUI program, obviously.) Let this stand as my to-do for that command-line utility.

Also: I think it's time to admit that I'm going to write the UI portions of the Xlat project in Decl, not plain Perl. This will probably require the definition of a Xlat::Declarative module. (That's a good thing.)