Add basics for ACIA 6551:w
Add ACIA Reset()
WIP
Add failing spec with chanels.
Implement acia 6551
Update Memory interface

Because io.Reader and io.Writer already claim the functions Read and
Write it was necessary to rename the Memory interface methods Read and
Write to ReadByte and WriteByte.
Add tests for cpu/acia integration
Merge pull request #3 from ariejan/issue_3_acia6551

Add support for 6551 Asynchronous Communications Interface Adapter (ACIA)