#10 (ColecoVision) Support MegaCart mapper

[clobber]

The MegaCart mapper supports bank-switching cartridges up to 1MB. More info here in the thread with attached PDF: http://atariage.com/forums/topic/216354-colecovision-megacart-faq/

Example implementations in other emulators:
* WiiColEm https://github.com/raz0red/wiicolem/search?l=c&q=megacart&type=Code&utf8=%E2%9C%93
* BlueMSX https://sourceforge.net/p/bluemsx/code/779/

Support would enable the following attached homebrew games to work:
* Princess Quest
* Pac-Man Collection
* Mario Bros.
* Zombie Near

[Lawrence Sebald]

Added in r263.

[clobber]

Thanks again for this! I tested all the attached MegaCart mapper games with r265 and they all run as expected besides zombnear.col, which just cycles through outputting garbage on screen.

I think it should run fine on real hardware and it at least runs with BlueMSX.

[Lawrence Sebald]

Zombie Near is indeed crashing (of course the one I don't test would be broken). However, I'm not entirely convinced that it is related to the mapper in use (the game appears to be properly setting the mapping up, as far as I can tell). To that end, I've opened up a bug (#43) for that particular game. Feel free to comment over there if you want to follow any progress as it might happen on that issue...