[pdal] Stage Naming Scheme

[Paul Ramsey]

So, looks like there's been some serious shaking of the user-facing
tree on the naming of stages. Since the documentation is now out of
date for LAS, before going and fixing things I'd like to understand
the overall scheme and plan.

For LAS I see this (new)

    SET_STAGE_NAME("readers.las", "Las Reader")

For PgPointCloud I see this (old)

    SET_STAGE_NAME("drivers.pgpointcloud.reader",

If the new scheme is that "readers should be called simply "readers""
then I'll also re-name all the reader stages before re-documenting.

Are there any other re-namings going on?

Thanks,
P.