fp-ieee: IEEE 754 operations for floating-point types

This library provides IEEE 754-compliant operations, including

• fusedMultiplyAdd.
• correctly-rounding versions of fromInteger.
• realFloatToFrac, which correctly handles signed zeros, infinities, and NaNs (unlike realToFrac).

Some operations (e.g. fusedMultiplyAdd) can make use of the native instruction in the architecture.

For non-native targets, "Pure Haskell" mode is supported via a package flag.

Most operations require only RealFloat constraint, but RealFloatNaN is needed by some operations that access the sign and payload of NaNs.