The VFP passes the two "I am the walrus" tests from RFC 8188.

The key table is currently just a mockup.

Including the length of the authentication tag.

Exposed a bug in padding that has been fixed.

rfc8188_test doesn't use it (since fixed salt values are given by
the examples), but calls it just to be sure that nothing blows up.

So the calling code doesn't have to.

Test passes for the example in RFC8188 ch 3.1.

Initially no VMOD, VFP or the like is defined, but code applying
libcrypto to implement RFC8188 is committed, as well as a test
program that checks the results against the two examples in
chapters 3.1 and 3.2 of the RFC.

The 'make' target currently doesn't do anything, but 'make check'
runs the test.