fix build to last Rust + rust-portaudio
- rust -> abs() is now a method of std::num::Float
- rust-portaudio -> small API change
remove warnings
- change missing_doc lint to missing_docs
- add rust-lang/time to cargo.toml
Merge pull request #51 from jeremyletang/update

update to last Rust + rust-portaudio
Updating to latest rust-portaudio
update to last rust-portaudio api + fix warning for unused results