licenses: convert license tags to SPDX
lib: move int bitwise lemmas from NatBitwise to Lib NB: this now imports HOL-Word into Lib and Lib in turn into NatBitwise.
autocorres, lib: refactor `nat :: bit_operations` instance This refactors the instances in HaskellLib and AutoCorres into a new theory, Lib.NatBitwise.