Reinstate pre-preparation of 64-byte md5 block.
Update test.sh to test a couple of extra files. (Not in repo.)
Allow linking with optional assembly language md5 routines
Extend use of pre-calculation for md5 hashing
Add "config.h" as Makefile dependency to trigger rebuilding
Code for using Solar Designer MD5 implementation
Add compilation instructions
Include MD5 functions by Solar Designer