Make sure all documentation examples build and run

[mjhouse]

I'm not sure that they do, currently.

[vcrn]

I suppose this issue more concerns manually checking that the examples do run when copy-pasted to a main.rs, but this library looks quite interesting for testing: https://github.com/dbrgn/embedded-hal-mock

I guess we could see if we can get some actual testing in place using that lib, if it seems useful.

[mjhouse]

Oh yeah. Sorry, this was drive-by issue. I didn't think of the fact that you would need hardware to run the doc tests. I may take a stab with the mocking lib at some point in the next few days.

[mjhouse]

I removed the good first issue tag, since this is going to be somewhat involved, and created #25 to investigate mocking for doc tests.