Use Cargo to run the benchmarks

Naming the benchmark folder benches instead of bench lets Cargo run the
benchmarks one by one like the test suite. The directory structure was modified
accordingly also getting rid of the now superfluous files.
Adapt Travis CI integration to benchmark change
fail! -> panic!
Merge pull request #136 from tomaka/master

fail! -> panic!
Removed constraints on ortographic projection function to allow bigger values for left, bottom, near than right, top, far.
Merge pull request #137 from Darkspear7/master

Fix for orthographic projection and removed constraints on input
Merge branch 'cargo_for_benchmarks' of git://github.com/aepsil0n/cgmath-rs
Improve the benchmark suite.

As a side effect, this adds `Rand` deriving to the benchmarked strucures.
Merge pull request #138 from sebcrozet/master

Add more benchmarks.