Better mod naming.

This patch does the following:
- Allows mod authors to provide a `mod_info.txt' file, to
  specify the mod name directly (and can later be used for
  other information about mods).
- Strips everything after the first dash. This makes it
  possible to have the `-master' suffix added by GitHub to the
  directory name.

This should avoid the need to rename the mod folders in
most cases (with the first point, in all cases).