New target: TRS-80 Color Computer 3

From now on, you can also play Lader on the  TRS-80 Color Computer 3 (coco3)!

Suggested emulator: xroar
Instructions: select the Tandy Color Computer 3 using the Hardware -> Machine menu; load the "lader.coco3.dsk" file and then issue the following commands:
DOS
LOAD"LOADER.BAS"
RUN