Ubuntu: Use code.iki.fi as the main APT repository

Dropbox remains as a mirror.
Ubuntu: Only include the latest changes in the package changelog
Builder: Encode tags in feed output

The tag with < and > characters was not tolerated.
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine
Builder: Use CDATA to encode characters in the XML feed
Revert "Homepage|CSS: Font readability tweaks"

This reverts commit 99fa47fba72876361e38d8df096bb0753720bb61.

These tweaks had adverse effects on non-Windows platforms that have
different font rendering capabilities.
Documentation: Cleanup
Merge branch 'master' into mapdata-c++