Merge pull request #16 from eddyb/update-for-master

Updated to current Rust master (no do for closures).
Build with --opt-level=3.
Merge pull request #18 from eddyb/opt-level-3

Build with --opt-level=3.
Added a new test to test PNG loading performance and two large test PNGs.
Merge pull request #17 from eddyb/test-perf

Added a new test to test PNG loading performance and two large test PNGs.
Upgrade to latest Rust.
Merge pull request #21 from metajack/rustup-20131219

Upgrade to latest Rust.
Use truncation on file create to avoid leaving trailing garbage
Merge pull request #22 from larsbergstrom/create_mode

Use truncation on file create to avoid leaving trailing garbage
Updated Rust
Added .rlib to .gitignore