Merge pull request #44 from cmr/master

Update to Rust nightly
to_str -> to_string
Merge pull request #45 from Kimundi/master

to_str -> to_string
Fix .travis.yml due to rust-lang/rust#14832
Merge pull request #48 from Kroisse/fix-travis

Fix .travis.yml due to rust-lang/rust#14832
Fix for lifetime elision