This commit includes changes that improve how and what Rocket logs
automatically. Rocket now logs:
* All guard errors, indicating the failing guard kind and type.
* A warning when a 'TempFile' is used as a data guard for a request
that specifies a 'form' Content-Type.
* Only the top/sub of a request's format.
This commit makes the following breaking changes:
* '<T as FromData>::Error' must implement 'Debug'.
Furthermore, this commit restores the previous behavior of always
logging launch info. It further restores the unspecified behavior of
modifying logging state only when the set logger is Rocket's logger.
The new examples directory...
* Contains a `README.md` explaining each example.
* Consolidates examples into more complete chunks.
* Is just better.
Resolves#1447.
Sergio Benitez