Remove unused imports
Add testsuite as a proper Cabal testsuite
Move testsuite source files to separate toplevel directory
Fix a bug in implementation of indirect addressing:
ZP wraps around, so if low part of address is stored in $FF, the high part should be looked for in $00
Use undefinedS instead of an arbitrary default value in memoryMapping
Be a bit more robust against undefined signal values
Fix the address of (@@),Y as shown in the Show instance of InitialState