Credited contributors and fixed lack of periods at the end of changelog lines.

I think the lack of consistency in periods at the end of CHANGELOG lines is embarassing :) Put them everywhere.

I also found from maintaining other OSS projects that putting the contributor's name in the end of CHANGELOG lines has encouraged others to contribute. I added them for the last release, although didn't have the energy to backport everything for the 10 releases prior. The format I use is:

```
[#PR](github link): Description - [@author](github link).
```