https://github.com/imageworks/OpenColorIO/pull/147
https://github.com/imageworks/OpenColorIO/issues/113

Split ColorSpace.family into ColorSpace.family / ColorSpace.equalitygroup

This allows one to distinguish amongst ColorSpace grouping suitable for
user interfaces, vs. ColorSpace groupings suitable for equality comparisons.
Both are now optional, which should lead to less confusion amongst users
crafting profiles.

Addresses issue #113

This may be the last conceptual change before 1.0 RC1 (all that
remains is minor API cleanup / documentation / testing)

-- Jeremy