Added Matrix3::from_diagonal

Useful for creation of scale matrices.
Merge pull request #110 from ZeronSix/scale

Added Matrix3::from_diagonal
Switch to cargo
Merge pull request #112 from bjz/cargo

Switch to cargo
Build benchmarks on travis
Merge pull request #113 from bjz/bench

Build benchmarks on travis
Remove deprecated functions from array traits
Use more self-explanatory names for indexing methods
Transition codebase to the new method names
Add fixed-length array conversions

Closes #111

`FixedArray::from_fixed` cannot yet be implemented due to  rust-lang/rust#16418
Merge pull request #114 from bjz/array-stuff

Array stuff