Release Version 0.0.1b16

What's New:

• Changed: RemoteServer.register(name, obj) now hosts only obj; use the new RemoteServer.register_recursive(name, obj) to also expose the world and nodes an env is built from (components mode).
• Extended space metadata vocabulary: frame, rotation, control, mode, normalized, range, names (plus per-element units), recommended kind values, the "HW" layout and "bgra" format.
• Metadata helpers: image_metadata, depth_metadata, proprio_metadata, action_metadata, metadata, annotate (attach metadata to nested spaces by path), validate_metadata / metadata_issues, common_metadata.
• Space.clip(x) on every space (#4): projects a value of a superspace onto the subspace, or raises ValueError when that would require inventing data.
• Fixes: combined world nodes keep the metadata of merged dict spaces; DynamicBoxSpace/GraphSpace subspace checks, GraphSpace.contains, UnionSpace.contains with NumPy integer indices; BoxSpace.clip dtype and 0-d results.

See CHANGELOG.md for details.