Metapost illustrations

I re-created most {1} of the hand-drawn illustrations using [Metapost].

The included ``Metapost-Illustrations.rst`` is the readme on how to build the illustrations.

A (temporary) [proof sheet] can be found at [this URL].

[Metapost]: https://www.tug.org/metapost.html
[this URL]: http://www.docdroid.net/addy/c101-vgfx-mproof.pdf.html
[proof sheet]: http://en.wikipedia.org/wiki/Contact_print#Proof_sheets
{1} what's missing from re-creations (so far?) are the DiffieHellman and PGP versions as well as the files that were already in a vector format to begin with.