Bugfix in opRand()

Change-Id: Icb42b973856dc6607cdb6b6069cd463694b66451
Implemented Math opcodes (8xxx)

Change-Id: Ie89a73eaf57b490c3ba018b2b5b32d34277f3f89
Implemented keyboard opcodes (and added keyboard field)

Change-Id: Ia49695b263e3de73a3b4ab0d6827df2c2c935ece