Documentation update for 3.4.0-YYYYMMDD releases

We should clean up some of the more problematic documentation issues.

- [x] The release notes are a bit of a mess (only found via the [wiki index](https://github.com/internetarchive/heritrix3/wiki/index)). Should we move them into a `CHANGES.md` file? Can we also pull in @kris-sigur blogs [1](https://kris-sigur.blogspot.com/2015/09/looking-for-stability-in-heritrix.html), [2](https://kris-sigur.blogspot.com/2016/04/new-semi-stable-build-for-heritrix.html) and get all the way back to the [Cookie Monster](https://github.com/internetarchive/heritrix3/pull/96)?
- [ ] The major 'front pages' should be reviewed to check they make basic sense and link to the right places.