Improve documentation about what CustomConfigHelperMixin does,
it was not very clear without a close look to the code before.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Introduce Changelog.draft.rst in the releasing process. Using a dedicated file
for the WIP gives more readable diffs.
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
