Implement command to write a byte to memory.
Implement command to write a byte to memory.

Fixes #64

KestrelComputer/kestrel,KestrelComputer/kestrel,8l/kestrel,8l/kestrel,sam-falvo/kestrel,8l/kestrel,8l/kestrel,sam-falvo/kestrel,sam-falvo/kestrel,KestrelComputer/kestrel,8l/kestrel,8l/kestrel,sam-falvo/kestrel,KestrelComputer/kestrel