Handle a loose directory of TBG files

[btigi]

While many TBG mods are single files distributed in a single TBG, or a collection of TBG (and other) files grouped into an IAP, there are a number of mods which are just a collection of TBG (and other) files in a directory.

weiduize should be updated to handle a directory of files, processing each TBG as encountered and generating basic COPY code for non-TBG files.