[WIP] Integrate BlueRov examples

[hamishwillee]

BlueROV have some useful examples in https://www.ardusub.com/developers/pymavlink.html that they have offered to donate.

Some of this would be useful in these docs, but integration is not so easy as:

1. Significant overlap with guide
2. This is very MAVProxy specific.
3. Pretty sub and bluerov centric
4. Need to make it as agnositic as possible to flight stack.

I'd also quite like to tutorialize the docs - split more into a very simple howto and some guide material. Right now the guide is actually good, but very dense.
Might be best to simply create a library of examples that people can use as they will.

But for now I'm looking at it and thinking - lots of testing needed. Not a priority now.

So, still thinking about this. This PR keeps me from forgetting about it.