Unix port doesn't include many circuitpython modules

[rhooper]

The unix port should have it's Makefile updated so that hardware-independent modules are included, so that tests can be added for them.

Please add modules you know can be added to the circuitpython unix port to this checklist.
We might also want to have a HAL that provides dummy hardware for testing code functionality too, but that will probably want a bunch of different issues.

• _pixelbuf