Add section on configuration in deprecation/backwards-incompatible changes
Added Quantity section to what's new
Re-wrote intro and added statistics of issues/PRs/contributors

The stats came from the script at https://gist.github.com/eteq/9faf252ec8aa41188dcb
Various what's new tweaks
Improvements suggested by @mhvk

[ci skip]
Merge pull request #2694 from eteq/whatsnew-updates

What's new for 0.4 updates