refactor lints into categories. lints are now more strict.

rust:
* ALL lints which rustc defaults to "allow" have been set to "warn".
* NEW "warn" lints which produce a warning as of this commit have been
explicitly identified and commented with a TODO for later review.

clippy:
* ALL categories (sans restriction) now fully enabled to "warn".
* redundant lints set to "warn" from categories now at "warn" are removed.
* previous "allow" sadness moved into respective categories.
* new warnings produced as of this commit have been explicitly identified:
	- nursery lints set to "allow" marked with TODO for later review.
	- pedantic lints set to "allow"

Signed-off-by: Jason Volk <jason@zemos.net>