Add driver to ohmd_list_gets, display device driver in simple example

[Aesthetikx]

This adds the OHMD_DRIVER to ohmd_list_gets to be more consistent with the ohmd_device_desc struct. This also displays that driver in the simple example. Reason I added this was for clarity; I was running the example on a laptop with no devices connected and was surprised to see devices connected. It is somewhat obvious that it is the dummy driver (and it says null device) but I think this improves clarity for newcomers and people possibly testing multiple devices or adding new drivers etc.

[TheOnlyJoey]

As this is a API addition, it needs to be put under consideration and merged at a good time.
I will bring this in the next API discussion and see if we can mark it for a release (0.4 probably).

[Aesthetikx]

As this is a API addition, it needs to be put under consideration and merged at a good time.
I will bring this in the next API discussion and see if we can mark it for a release (0.4 probably).

@TheOnlyJoey Agreed, same can be said about #284 if you like any of those changes.