Add #![allow(unknown_features)] for #![feature(slicing_syntax)]
Merge pull request #154 from XiaonuoGantan/master

Add #![allow(unknown_features)] for #![feature(slicing_syntax)]
Fix for latest rustc: static => const
Fix tests: Add #![feature(slicing_syntax)]
Merge pull request #156 from ljrmorgan/master

Fixes for latest rustc
strftime now returns Result, so unwrap()
Merge pull request #158 from excepttheweasel/fix_for_strftime_result

strftime now returns Result, so unwrap()