Upgraded to latest gl-rs
Merge pull request #336 from Coeuvre/master

Upgraded to latest gl-rs
Upgraded to latest Rust-Empty
Merge pull request #337 from bvssvni/master

Upgraded to latest Rust-Empty
Added links to docs for sdl2_ttf and cgmath

Closes #340
Merge pull request #341 from leonkunert/master

Added links to docs for sdl2_ttf and cgmath
Added portaudio and SoundStream trait for real-time audio IO. Example included.