risk/writers:

Added LossMapGeoJSONWriter, which is basically the GeoJSON equivalent
of the LossMapXMLWriter.

I also abstracted a base LossMapWriter class to share code common to
all such writers.
tests/risk/writers_test:

Added tests for LossMapGeoJSONWriter. Also some minor tweaks to the
LossMapXMLWriter tests.
risk/writers:

pep8 whitespace cleanup
risk/writers:

Updated the LossMapGeoJSONWriter to use a slightly cleaner way of
serializing to a file.
hazard/writers:

Factored out HazardMapWriter base class from HazardMapXMLWriter.
hazard/writers:

Added HazardMapGeoJSONWriter class.
tests/hazard/writers_test:

Added tests for HazardMapGeoJSONWriter.
hazard/writers:

When building the metadata dict for hazard map geojson outputs,
don't include attributes which are None/irrelevant.
Merge pull request #99 from larsbutler/geojson-lossmap-writer

GeoJSON LossMap Writer

[r=micheles] [f=1198881]
Merge pull request #100 from larsbutler/geojson-hazmap-writer

Hazard map GeoJSON writer

[r=micheles] [f=1199655]