eval-after-load now uses 'tex feature.

This is used instead of the file name (as a string).
Whoops, text in todo in wrong spot.
Complete `toggle-plural' library.

I deleted all the half-right code, added docstrings, and made it pass
checkdoc.
Remove useless comment.
Add autoload cookie.
Add use-package declaration for toggle-plural.

Also add a binding to `C-c C-s'.