Drop-in std::map replacement support

[JWCS]

This library looks great, as the only maintained c++ ordered map library. However I was trying to use it as a replacement in a large codebase that had only key-ordered std::map, and the compilation errors were extensive. This is with cutting down the template types to the first 2 commonly shared ones, and stubbing any functions that weren't implemented between the two. While it would be a good bit of boilerplate, since this library is so close, all the functionality is there, it'd be nice if there was an out of box compliant mode (even if behind macro flag).