Release 1.1.0

Summary:
This release adds a Perforce provider* and corrects the git provider
behavior when using `ensure => latest`.

*(Only git provider is currently supported.)

Features:
- New Perforce provider

Bugfixes:
- (MODULES-660) Fix behavior with `ensure => latest` and detached HEAD
- Spec test fixes
Merge pull request #196 from hunner/release_1.1.0

Release 1.1.0