Added operations to convert sequences of features to geojson
Fixed bug with .mapIfSet in StrictRasterData\some ArrayRasterData types.

Fixes #545
Merge pull request #546 from lossyrob/bug/mapIfSet

Fix mapIfSet bug, add additional ToGeoJson operations.
Benchmarks now use singleton Server.

The benchmarks were broken because multiple Server instances with the same
identifier were being instantiated at the same time.  This fix allows
the benchmarks to run once again.

Fixes 547.
Merge pull request #548 from joshmarcus/issue/547

Benchmarks now use singleton Server.