Add implementation details and other things

[piegamesde]

I spent two hours reading issues and discussions so I thought I may as well put another two hours into writing down their conclusions (or at least what I think).

Any of the commits may be discussed separately and I'm open to create a distinct pull request for each if there's need for it.

This addresses topics from #150, #51, #148 and probably a few others.

[piegamesde]

Thanks for correcting the typo. Currently, the convention doesn't say anything about any changes or reconfiguration. I just thought it would make writing Homie-Controllers easier if they didn't have to be aware of any device changes all of the time (It may also make writing libraries easier). I remember some discussion about adding an explicit reconfiguring state, but I think a simple reconnection or using the init state should be enough.

[mjcumming]

I think that makes sense. I'll let @Thalhammer weigh in on the proposal before approving.