???: embedded comments into volume_mask_dict for TODO (+ minor code changes and DOC changes)
Merge branch 'enh/surfing' into _tent/surfing
BK+API: rename "aux_get" to "get_aux"
DOC: more documentation and some answers to issues raised by Yarik
BF: return proper meta data even when set to False or None
BF: return proper meta data even when set to False or None
DOC: explain why use of "merge" instead of "update"
RF: use get_aux instead of deprecated aux_get
NF+BK? more efficient storage of voxel selection results as suggested by Yarik
TST+NF+ENH: test "old-style" (pre-Dec 2013) way of storing and loading voxel selection results to disc, and separate the "old" logic from the "new" using a separate _setstate_legacy method
DOC: minor explanation of rationale of testing legacy voxel selection storage
RF: seperate __setstate__ functionality in _setstate and _setstate_legacy (the latter with deprecation warning)
BF: fixed typo
ENH: support merging of voxel selection results even if they have different subtypes (e.g. float32 and float64)
ENH: more verbose information when object is tried to be "__reduce__"d
BF: use internal _add_fa instead of attribute add_fa
RF: move conversion to/from tuple representation of dict-with-arrays outside of class
NF: __str__ for surface query engine
NF: seperate __reduce__ in legacy form + unit test