[Cryptech Tech] core reorganization

[Paul Selkirk]

We just reorganized the repositories under 'core'. Instead of the flat
organization, repos are grouped by function so it's hopefully easier to
figure out what's what. Plus, the EIM code is fully integrated, and
bogus/unused/ancient repos are removed.

The new organization is:
core/cipher/aes
core/cipher/chacha
core/comm/coretest
core/comm/eim
core/comm/i2c
core/comm/uart
core/hash/sha1
core/hash/sha256
core/hash/sha3
core/hash/sha512
core/math/modexp
core/platform/common
core/platform/novena
core/platform/terasic_c5g
core/rng/avalanche_entropy
core/rng/rosc_entropy
core/rng/trng
core/rng/vndecorrelator

You can either re-fetch the repos under the new names, or use `git
remote set-url` to redirect your local copies.

The old repos will be available in a read-only 'historical' location;
Rob will send details when that's set up.

				paul