Instruction test cases

[suborb]

In case it's useful, I've put up the instruction test files that I used during development. They can be
found here: https://github.com/suborb/vasmz80_testcases

[rgiot]

Marvelous !
I'll look on that within the week in order to integrate them.
If you prefer, you can do a pull request which integrates your test cases if you want the job be done faster