Add set_all_channels() for setting on, off counter values and full-on and full-off in one transaction

[mhthies]

Follow-up and alternative solution to PR #17. See discussion over there for detailed description of the problem and advantages and disadvantages of the solution approach.

[coveralls]

coverage: 83.103% (-0.8%) from 83.883%
when pulling 29d017f on mhthies:feature/set_all_full_on_off_2
into 9865710 on eldruin:master.

[eldruin]

Great, thank you!
Could you also add an entry to the changelog?

[eldruin]

Sorry, could you also briefly explain this function in the readme/lib.rs like the rest?

[eldruin]

Could you run cargo fmt again?

[mhthies]

Done. Sorry for not checking this. I ran cargo doc, but I didn't consider that cargo fmt might dislike a random extra space in the comment.

[eldruin]

I have published this in version 1.0. Thanks!