Add test for correct frame buffer output

[BenShelton]

This adds a new test to check that the frame buffer is actually generating the correct frames using the existing Croom.nes ROM. Some files will load and generate "frames" and a "frame rate" but will become stuck at the initial screen (a black border and grey box). This test helps to detect this issue (originally reported as #113)

This also fixes the file loading in the test cases to use binary instead of ascii encoding which causes the problem.

The test works by checking the first index of a certain color pixel (white) on the first 6 frames of output. Croom only uses 2 colors on the initial screen which makes it easy to detect. Comparing full snapshots of each frame takes too long.

[bfirsh]

Super cool, thank you so much!