Close 164 and 165

[pdarragh]

Adds instructions:

• Jz
• Jnz
• Cmovz
• Cmovnz
• Shl
• Shr

Updates documentation accordingly.

Documentation also extended to explain the FLAGS register more explicitly, and instructions that modify the flags are explicitly annotated.

[pdarragh]

I added the -z-suffixed instructions because (a) I already support them in cmsc430/a86-interpreter, but (b) I think it helps when the other three supported instructions share a name with their flags already. Then we can just say the -e suffix is an alias for -z, which makes sense when Cmp is used due to the nature of subtraction.