Expose unchecked shift methods

[oscbyspro]

I've already exposed them in Numberick, but I aught to do it here as well. It's probably more important here because it's not possible to efficiently mask non-powers-of-two. See (#130).

[oscbyspro]

Hm. I suppose I managed to precondition these methods in Numberick whereas bounds checking is much worse here.

[oscbyspro]

mutating func bitshiftLeftSmart(by: Int)
func bitshiftedLeftSmart(by: Int) -> Self

mutating func bitshiftLeftUnchecked(by: Int)
func bitshiftedLeftUnchecked(by: Int) -> Self

mutating func bitshiftLeftUnchecked(words: Int, bits: Int)
func bitshiftedLeftUnchecked(words: Int, bits: Int) -> Self

mutating func bitshiftRightSmart(by: Int)
func bitshiftedRightSmart(by: Int) -> Self

mutating func bitshiftRightUnchecked(by: Int)
func bitshiftedRightUnchecked(by: Int) -> Self

mutating func bitshiftRightUnchecked(words: Int, bits: Int)
func bitshiftedRightUnchecked(words: Int, bits: Int) -> Self