Right shift and division with rounding.

[stephentyrone]

Fairly correct implementation of right-shift and division with rounding. Also fairly efficient, though I'm sure I'll find some cases where we're generating uncessary overflow checks upon further inspection. Nonetheless, a decent enough start.

The methods are added to BinaryInteger:

• shifted<Count: BinaryInteger>(right: Count, rounding: RoundingRule) -> Self
• divided(by: Self, rounding: RoundingRule) -> Self

The following methods are added to SignedInteger (not BinaryInteger, because the remainder is not generally representable in an UnsignedType when the rounding mode is not .down or .towardZero):

• remainder(dividingBy: Self, rounding: RoundingRule) -> Self
• divded(by: Self, rounding: RoundingRule) -> (quotient: Self, remainder: Self)

The following free function is added:

• euclideanDivision<T: BinaryInteger>(_: T, _: T) -> (quotient: Self, remainder: Self)

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test

[stephentyrone]

@swift-ci test linux