bump minor version (rust-windowing#468)

* bump minor version

* update changelog date and fix typo

* Updated date (we're going to release for real this time)

* Update version in README for the first time in a long time

Publish 0.6.4

Merge pull request rust-windowing#160 from mitchmindtree/publish

Publish 0.6.3 with recent non-breaking macOS fixes