Merge pull request #596 from bvssvni/master

Fixed unit tests
Remove old Matrix2d replaced by vecmath::Matrix2
Merge pull request #597 from lucidd/master

Remove old Matrix2d replaced by vecmath::Matrix2
Add rust-ci
Merge pull request #598 from Indiv0/add-rust-ci

Add rust-ci
new rustc
Merge pull request #599 from bfops/master

new rustc
Fixed a bug of `flip_h` of trait `RelativeTransform2d` in `relative.rs`
Merge pull request #600 from Coeuvre/master

Fixed a bug of `flip_h` of trait `RelativeTransform2d` in `relative.rs`
Remove Rust-empty
Merge pull request #601 from Indiv0/remove-rust-empty

Remove Rust-empty
Removed xy_64 methods in BackEnd

Closes https://github.com/PistonDevelopers/rust-graphics/issues/602