Add simple housenumber handling for OSM data

Housenumbers that are tagged with addr:housenumber and add:street are now applied. It can be enabled with the undocumented parameter --x-housenumbers. It's not yet an official parameter because it handles only a small subset of housenumbers.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2485 25d90789-57f7-4ee0-8453-03a3dfeeeb22
Add filter for shapes to remove obsolete points on straight lines and spikes.
This has no visible effect but reduces the img size a little bit.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2486 25d90789-57f7-4ee0-8453-03a3dfeeeb22