Release 1.8.0

- Run all `cake doc:*` tasks.
- Gone through all [commits since 1.7.1](https://github.com/jashkenas/coffeescript/compare/1.7.1...master) and added everything worth noting to the changelog. I tried to make each entry short. Please tell me if I’ve missed something, if something is too minor to be mentioned and if something needs rewording.

Note that I’ve set the release date to 2014-08-26.