A partial implementation of the SHA1 cryptographic hash algorithm, one
cycle per SHA1 iteration.

This is a PARTIAL implementation, computing only one 512-bit SHA1
block only, so is suitable for hashing only very short messages.  It
does not do multi-block chaining as is required by the specification.

Note that SHA1 is now a broken hash algorithm, and should not be used
for new applications (in favor of SHA 224/256/384/512, and the
upcoming SHA-3 standard).



I think it can still be improved by (1) marking the multiple cycle
rules mutually exclusive, and (2) allowing the next block to be
enqueued immediately after the first completes, instead of a one cycle
rest while in Invalid state.