Additional utility APIs

[james7132]

This PR adds the following APIs, and refactors a few existing ones to use them as implementation details:

• contains_any_in_range - Checks if any bit in a range is set.
• contains_all_in_range - Checks if all bits in a range are set.
• minimum finds the smallest bit that has been set, if any are.
• maximum finds the largest bit that has been set, if any are.
• is_full checks if every bit in the bitset has been set.
• count_zeroes is the corollary to count_ones, where it counts the bits that haven't been set in a range.
• remove_range clears a range of set bits. set_range now just chooses between insert_range and remove_range internally. Moves the branch out of the loop.