Doc page with extinction examples

[tpoisot]

@evadelmas / @TomClegg94

I'm ready to merge next into master and go forth with a new release (when #40 is done) -- before we do this, the doc needs a page about extinctions.

I added an empty file at docs/src/man/extinctions.md -- please add something short and sweet.

Great work all around.

[CleggTom]

I've added the beginning of the docs with #42.

We still need to add the various rewiring parameters as a docstring somewhere. It's not exactly clear where though as there is no rewiring_parameters and the make_parameters docs are fairly long already.