Investigate using embedded-hal-mock for examples

[hannobraun]

A lot of this driver's API doesn't have examples, because writing them would be tedious. There are some examples, but they contain their own stub implementations of embedded-hal traits.

I believe both of these issues could be improved using embedded-hal-mock. By mocking embedded-hal traits, we should be able to write API examples that are relatively straight-forward.

The actionable items here are:

• To investigate whether this is really the case that embedded-hal-mock cloud help here.
• Extend embedded-hal-mock. I don't it implements all the traits we require.