Changes to base

Changes to base:
commit 63f669b9385bbaba32b0fc20bf16f8a8d96ddfa3
Author: Herbert Valerio Riedel <hvr@gnu.org>
Date:   Wed Jan 29 13:53:27 2014 +0100

    Add Hackage-supported `changelog.md` file

    The contents has been ripped from the release notes. I've used markdown
    as this may allow for automatic conversion to docbook XML in the future,
    should we choose to maintain the `base` changelog in a more human-friendly
    markup format and closer to the `base`-source tree.

    Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>