Rough initial port to PDAL point-context-schema.  Need to advertise Dimensions to a client, and allow them to specify a) which they want and b) how they want them.
Prep for creating a real schema transfer and selection protocol.
Update unit tests with point-context-schema changes.
Plumb a Greyhound schema request and its handling into the C++ addon.
Route Greyhound schema request through the rest of the server and update unit tests.