Merge pull request #6 from MapQuest/mla-group-symbolizer

Added a couple of tests, fixed a bug.
Merge pull request #7 from MapQuest/mla-group-symbolizer

Cairo implementation of group and debug symbolizers.
Merge pull request #8 from MapQuest/mla-group-symbolizer

SVG renderer
Grid renderer implementation for group symbolizer, with visual test case references
Merge common group symbolizer processing code from individual renderers into renderer_common
Merge pull request #9 from MapQuest/mla-group-symbolizer

Python interface for group symbolizer.
Merge pull request #11 from MapQuest/jmh-group-symbolizer

Grid renderer and combining more code