A Coin is data type for representing Boolean values that is resistant to bit
flips. Prefer Coin to bool in safety-critical environments with long-lived
variables, such as global variables.
A standard bool is truth-biased, because false matches a single bit pattern
(all zeros). A single bit flip invalidates the value. Coin counts the number
of bits to determine its truth value. When 4 or more bits are 1, the value is
interpreted as true. Coin can tolerate 3 bit flips per byte before an
incorrect value is returned.