Changelog, RST and declaring dependencies

## On docs/HISTORY.txt vs CHANGES.txt

I'd actually prefer CHANGES.rst - the extension .rst for better syntax
highlighting (we have those files in ReST anyways) and CHANGES in the
package's top level directory, because we actually document changes
between releases and have not an historic essay. It just names the
purpose better, I'd say. I'm a non-native English speaker, so I might
be wrong.
docs/HISTORY.rst would be good for very long CHANGES.rst files, where
we might want just to have the changes since the last major version
release in.


## Prefer .rst over .txt for any documentation, even doctests
Just because of the nice syntax highlighting.

## Notes on how to declare dependencies