Release 1.0.0-rc.1 (toml-lang#720)

* Add TOML 1.0.0-rc.1

* Update README notice, for 1.0.0-rc.1

* Fix link to logo

* Update CHANGELOG to reflect release

Release v0.5.0.

Release v0.4.0

Release v0.3.1

Release v0.3.0

Release v0.2.0

Release v0.1.0.