Move exp into its own repo

[kortschak]

The principle for the existence of exp is that breaking and breakable things can be done there. This is in contrast to the other repos that should always pass on master.

Because of this, I would like to see experimental code be played with somewhere else, ausocean/exp so that build failures on production repos are meaningful.

[Alan Noble]

I think this is a good suggestion, but other repos have experimental stuff too though, so ausocean/exp requires a structure that accommodates that, e.g.,

ausocean/exp/av
ausocean/exp/iot
ausocean/exp/iotsvc