Rework the directory structure into something saner, with src/ test/ include/ and build/

Beginning some tests.  Also, now support scan-build.

Now support 32-bit including vectorless ARM.  NEON is not yet supported, because I don't
have a test machine.

Many internal changes, improvements, and bug fixes.

Fix some doc copypasta on goldilocks_verify.

Changed the formats of private keys and shared secrets.

Added SHA512 support.  It's slow and probably has endian bugs.

Signatures are now supported.

Renamed a bunch of internal functions to be more readable and
consistent.

Began documenting functions with Doxygen.

See HISTORY.txt for more details.