Prepare 0.6.0 release

Add new APIs from Windows SDK

Prepare 0.5 release

Release version 0.4.0

Bump version number

This version contains breaking changes because of `&mut self` -> `&self` in interface methods.

Merge pull request #37 from Boddlnagg/master

Toast notification example & bugfix

Merge pull request #33 from Boddlnagg/featurenames

Change Cargo feature names to use dash, add Cargo categories and bump version.

Mark more functions as #[inline]

... to make better use of recent rustc compile-time improvements