Add alt diagrams

[OR13]

[thomas-fossati]

Good start!

Immediate comments:

1. imprint must be messageImprint (from RFC3161)
2. Adding "Clock" is like dissecting a frog, innit? :-) (we can add a legenda as in Move detailed diagrams up a level #30)
3. The Signer box in the TTC diagram is a bit too crowded and hard to grasp
4. the fact that private-key is repeated is confusing
5. I am not yet sure if I like the stray unprotected box, but I could be convinced otherwise

[thomas-fossati]

Also, maybe rename them to alt-{ttc,cct}.ascii-art and tweak the include directive.

[thomas-fossati]

Thanks @OR13 - I have pulled your nice diagrams into #30

This PR is closed as a consequence of the above.