Allow rvalue_refs to be used with push and update methods (update, increase, and decrease)

Currently, only `emplace` has move semantics with regards to adding or updating the values in any of the heaps. This is limiting when the `value_type` is move only, especially as there is no workaround for the update methods. (`emplace` will invoke the move constructor, so it can be used as work around for `push`.) I propose adding overloads for the adding or updating methods to allow for values with move semantics to be used, e.g.

`handle_type push(value_type&&);`
`void update(handle_type, value_type&&);`
`void increase(handle_type, value_type&&);`
`void decrease(handle_type, value_type&&);`
`void update_lazy(handle_type, value_type&&); // fibonacci_heap only`

A similar issue exists in #23 for dealing with the comparison function.

Start by locating the existing emplace, push, update, increase, and decrease entry points across the heaps, including update_lazy for fibonacci_heap. Compare their current value_type handling and identify the related tests, then verify that each proposed rvalue-reference overload works with move-only values without changing existing lvalue behavior.

Written by the indexing model from the issue text.