ratcatcher/doco/adding_a_sprite.txt

- in defs.h: increment MAXPTYPES
- in defs.h: add P_ entry 
- in shared.c: add score value in setdefaults if applicable
- in shared.c: add loadspriteimage() line(s) in loadimagesets()
- in shared.c: IF NOT AN EFFECT: add entry to monstertochar
- in shared.c: IF NOT AN EFFECT: add entry to chartomonster
- in shared.c: update isflower(), isfruit(), isbullet(), iseffect();
- in shared.c: IF A GEM: update flowertogem()
- in rc.c: update ismonster()
- in rc.c: add monster movement