This commit makes it possible to build, document, and test Rocket v0.4.
The main changes are:
* A `Cargo.lock` was added that includes references to yanked deps.
* The `tls` feature isn't tested as `ring` fails to build.
* The site guide was moved to `docs/guide`.
* The `site/` directory was removed.
Remove form_items function in favor of FormItems iterator.
Add specialized `bool` implementation of FromFormValue.
Add `&str` implementation of FromFormValue for debugging.