* Add Eq instance for Ctx
* Add start and startlazy producing Ctx
* Introduce new use-cbits cabal flag in order to add support for
FFI-less cryptohash-sha256-pure pass-thru
A practical incremental and one-pass, pure API to the SHA-256
cryptographic hash algorithm according to FIPS 180-4 with performance
close to the fastest implementations available in other languages.