`drasil-system`: Create SmithEtAl-style software requirements specification encoding.

[balacij]

Contributes to #3260 and #4304

[balacij]

Just before anyone reads the code, one note: I'm pausing work on this because I'm not so sure this is the right design yet. I'll try to write out some thoughts on it later.

[JacquesCarette]

This definitely needs design first. I think the SmithEtAl format should be seen as exactly that, an output format.