Support other locked-on games

[FlitPix]

If games other than Sonic 1 are locked-on, a single special stage can be played. I would like to support this use case, even if it's not likely to be used often.

Details:

• If RAM 0xFFA0 is 1, Sonic 1 is locked-on. This might be useful if I want to handle this use case differently, but I probably don't.
• Locked-on ROMs over 2MB in size will not work and just boot into Sonic & Knuckles. [1]
• One possible worry design-wise is that one could find an easy stage and play it over and over for a bunch of hints. This theoretically is even worse if the stage is of a higher difficulty and/or easy to perfect, once Weigh progression and non-progression hints #1 is implemented. I won't be preventing this, for a few reasons:
  • This is not as fun imo, which inherently discourages that.
  • This can already be done with Sonic 1 locked-on using level codes.