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.

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.