Extract API spec into own document.
Docs: bring API docs up-to-date; expand thoroughly.
Docs: minor formatting fixes.
Routes: move into proper file, as-are.

But fix indentation -- standardize on four spaces.
Routes: remove unversioned API route.

Now that we need Zoom.it/v1 back-compat;
we should keep the versioning scheme for v2.
Routes: add error message constants.
Routes: fix bugs, impl. more API, improve code, etc.