Behavior of == when isless or < is defined

@Tamas_Papp in that case, I stand corrected. Users have to implement == and hash. Because there are cases where == should not behave like ===. Below is an example.

https://github.com/sambitdash/IntervalTrees.jl/commit/ec83e2a49123683ac786bd27e472455501a7e15d