Force HTTPS URLs, drop CSS Forms, add specs (#64)

* Force HTTPS URLs, drop CSS Forms, add specs

This update contains the following changes:

- HTTP URLs from the W3C API and Specref are now automatically switched to
HTTPS URLs. Switches get reported as warnings to the console. See #55.
- CSS Forms Styling was dropped. See #56.
- W3C API redirect reponses generate a proper error message. See #60.
- A number of missing specs signaled in #58 have been added.
- A couple of tests were added to detect shortname collisions, and the presence
of non-HTTPS URLs in index.json

* Add index.json (needed to make tests pass)

Previous commit changed the constraints on index.json so new file needs to be
included in the PR.