PDP-11 Emulator

I started a new emulator experiment, this time a PDP-11. The goal is to eventually be able to run Unix but that requires additional emulated hardware support. This first released version is able to run the original Tetris which is good enough for now. The result is an emulator that is kind of like a PDP-11/40, with the EIS and FIS instruction sets, but without the MMU support.