Initial commit; start with copy of btree_set_index.hpp
Oops! Start work on btree_map_index.hpp, and notice that btree_multiset_index name is misspelled. Commit before switching back to develop to deal with that misspelling (and lack of tests that would have detected the misspelling).
Merge branch 'develop' into feature/btree_map_index
Add class btree_map_index, class btree_multimap_index. Trivial test passing.
Fix a cut-and-paste error in btree_multiset_index. Add some tests. All four index types passing insert tests. Dereferencing iterators not working.
Work in progress before converting IndexTraits to a template template parameter to support maps.
Sets passing, maps commented out.
btree_map_index and btree_multimap_index passing preliminary tests, including iteration and dereferencing, for both fixed and variable length types.