Utility class for mapping Blender frames to a generic time scale.
This is used by writers and readers to convert frame numbers into time
values for the Alembic time sampling methods.
Removed the types.h file, not used and doesn't have a clear purpose.
Basic point cache reading for particles.

This currently requires exporting the Alembic archive. The automatic
caching is not yet implemented and may require some changes to account
for the sequential write limitations in Alembic and do some stitching
of old/new cache files.

Error handling is also rudimentary atm, the reader ErrorHandler::Policy
is just verbose printing atm. This happens a lot during export.