Fix contributions link in API bindings docs

Closes #286
Fix link to dev blog in contributing docs

Closes #287
Replace run-on sentence with two seperate ones

As suggested in 4e0fdf8.
Change examples to za-peoples-assembly

Replace kenyan-politicians examples with za-peoples-assembly ones.

I also removed the note on the URL potentially 404ing if the data has reloaded, as that seemed more of an issue for auto-generated IDs than pre-constructed ones.
The API now returns membership information

Update the example JSON responses to show the membership information that is now included.
Remove quoting of slashes

Some links had needless \/s
Replace links to components list

Point at the Poplus mailing list rather than the old Components list.
Improve data-import documentation

* Fix broken link to /migration (fixes #317).
* Add link to the API docs.
* Small text tweaks.