update automatic main.asm insertion

This updates the automatic parsing of main.asm to catch cases of INCBINs
pulling in files that end in .asm, .lz, .1bpp, and .2bpp. This is
necessary because otherwise the parser tries to figure out the start and
end addresses expressed on the INCBIN line, details not present on these
types of lines in the asm.

Asm and Asm.insert_all are now back in working condition.
update gbz80disasm for handling known fall-throughs

When disassembling a group of functions, sometimes there are other
functions known in advance. By passing in a list called stop_at to
gbz80disasm, it is possible to prevent disassembled asm from running on
for longer than necessary.