figure out an easier way to add new/alternative versions (aka better support for trials)

[DankRank]

There are many instances where we don't support the trial versions:

• th19 trial ANM have the extra fields in sprite_t, but not the PNG/JPEG compression as used in the full version
• th09 trial Plus DAT has to be extracted with -x8 because of different crypt_parms
• at least one trial (forgot which one) has differences in ECL signatures

It'd be nice to be able to add these things without having to add a new flag or having to come up with another version integer and updating all the NEWHU: places. I'm thinking each version should have a struct containing all the necessary info for a given program (stuff like th{ecl,msg,dat}_module_t, format lists, crypt_parms, flags specifying minor changes in the format, etc), and the version integer (or string) would be mapped to one of these.