Update Pebble effects, add unequip function, etc.

Modified "cast_spell_on_npc" such that elemental Pebbles always apply
their status effects, added an "unequip_heavy_item" function for
unequipping via pointer to a heavy_item_t rather than referencing an
equip target, updated "strcat_item_name" and "init_player", and
commented out large swaths of "draw_cell_contents" for testing purposes.