cubehash: new hash algorithm
cubehash: remove forgotten debugging
algos_enc: new cubehash-based algorithms
algos_sig: new cubehash-based algorithms
cubehash: some basic optimization
keyring: use cubehash for KeyID

This creates incompatible keyrings, so keyring identifiers now have a
version string appended to them.
build: crypto++ support is now optional

possibly also evading "traditional" hash functions. Cubehash is good.