Add a simple data tool, inspired by json.tool.

Serializes records to GeoJSON or dumps description information
as text or JSON.
Change record output to strict GeoJSON.

Meaning features in a FeatureCollection.
Let outfile be file or stdout.
Add an option to buffer writes at the feature, not colllection, level.
Pull write of GeoJSON head out of the try block.
More efficient identation and a few programming notes.
Add skipping/logging of errors and remove some short option names.

Until we figure out what the right short names are, we'll go with long names
like --compact, --encoding, --ignore-errors.
Expose the fiona tool as dumpgj.