Too many clippy warnings

Currently, running `cargo clippy` on `nalgebra` yields 581 warnings.

A few of these are false positives, and some others are just complaints about the complicated types of `nalgebra` (for which not much can be done). However, many of these should be strictly good improvements to the code. Many of these fixes would also be breaking changes, so we should be aware of that.

I believe that all of these warnings should either be fixed or turned off. That way, if any future sub-par code props up, we'll quickly be able to detect it and fix it.