Extra safety belt for binary-heap constructor
Binary-heap: refactor out the _maxIndex method
Binary-heap: avoid capitalized names for non-classes
New giant randomized test with self-checks
Fix the removal and the priority of _maxIndex.

Removing an arbitary element you might need to upHeap the position of removed
element instead of downHeap. It is not the case with the maximum, because root
can't be upHeaped.