Fix missing entry from examples Makefile

In the refactor I must have lost it somehow.
Add basic production & development requirements files

I'm not sure exactly how best to handle these but it seems like a good
step forward to have them somewhere.
Switch change log entry to Added

As people who want to use it will have to specify the future breathe
3.1.0. If we leave it as a bug fix then they'd have to specify 3.0.1
which isn't the point of patches.
Add changelog entry for headings support

Thanks to rweickelt for this.
Merge branch 'fix'