Cleanup minor issues in rest_api.md

- Spacing is now more consistent
- A few calls were slightly rearranged
Make the 'group' parameter explicit

I think this way is clearer, and it's actually shorter too.
Change 'label' to 'id' in rest_api.md
Add missing API calls to rest_api.md

Some of them don't have an obvious REST interface---those are marked at the
end.
Miscellaneous fixes to apidesc.md

These are similar to the changes made to rest_api.md.
Fix small typos in node_{register,delete}_nic
Revert 3340d0a

Change 'id' back to 'label' in rest_api.md
Also let 'id' -> 'label' in apidesc.md
Merge pull request #122 from gsilvis/doc-api-cleanup

Doc api cleanup