Reinvented successor & predecessor functions to allow simple incrementing/decrementing on non-random access iterators. Removed unneeded/duplicated template typedefs.
Added triple structure, analogous to pair. Added unit tests to check relational operations; note that because of difficulties in getting the constexpr mechanism to work I resorted to macros to paste in constexpr array lookups as a way to get different values into the template function
Start adding range algorithms and the unit tests