v2.1.0

Faster multiplication. Better testing. A fix thereof.

• #104 Fixed-width bitwise inverse of isZero
• #103 Faster signed multiplication
• #102 Low Signed/multiplyFullWidth(by:) sign
• #101 Denormalized Signed tests
• #99 Simultaneous non/mutating tests

New ANKFixedWidthInteger getters

var  isFull: Bool { get }
func matches(repeating bit: Bool) -> Bool