README: add both autogen.sh and configure to compiling instructions

The advice about running `./configure` only really applies if you got
the sources from a tarball (packager-friendly). Use both `./autogen.sh`
and `./configure` instead, to make it more developer-friendly.
Merge pull request #181 from knocte/master
Frontend-SWF: Use system colours
Frontend-SWF: Stubby but functional topic support

It's not exactly the best, but it's a start. Third try for style compliance.
Merge pull request #124 from NattyNarwhal/swf-fixing
Engine(-IRC|-XMPP): implemented engine/protocol-manager/on-presence-status-changed hook point