get rid of different heaps; use only binary sort

[mpadge]

Coz i'm pretty sure nobody uses them anyway, and the differences are very generally extremely minor. It was interesting to start with, but reducing to binary heap will simplify the code quite a bit, plus avoid using the shared_ptr between the heap types and so allow proper templating of types of heap variable. That will in turn make #90 more straightforward.

[mpadge]

Reference #137, and the importance of templating both <int> and <double> for sorting, to take advantage of speed gains in the former case.