Create small debug dataset

[rdadolf]

We can't expect to distribute real datasets. First, they're hundreds of GB, so it's a logistical headache. Second, we don't have the license approval to do so, even if we could.

Two parts to a solution:

1. Enable the use of large datasets when/if they're available.
2. Distribute a smaller datasets which we can give out. The performance will be wrong, but it should work. As a bonus, it'll make debugging tools and writing modeling tests easier.

[rdadolf]

Atari will be a problem, since it's highly unlikely that we'll be able to generate a test ROM. The best solution I can think of is probably to use a non-ALE debug input (i.e., a class which emulates the emulator API and pretends to be a game). Alternatively, we can simply not provide one for atari, but I'd rather have that as a last resort.