Add "CPU Integration Tests"

[x93bd0]

Checklist

• I believe this feature/suggestion would be benefitial and/or necessary to this project.
• I have searched for the same request on the issue tracker.

What's your idea?

As of now, we only have NESTEST for testing the CPU, but NESTEST lacks tests for every illegal instruction.
Also there may be a lot of weird combinations of parameters for the same instruction that aren't being tested.

Tests

• nestest
• cpu_dummy_reads
• cpu_dummy_writes
• instr_timing
• instr_test-v3
• instr_test-v5
• instr_misc

Why would this be necessary?

This will make CPU changes more easy to maintain, as it will remove errors that may appear after any optimization.