doc/: + "Drawing cells corner-by-corner"

As announced in [#3](https://github.com/tjohnman/KNOH/issues/3#issuecomment-28255654) here's my thinkings re how to do systematic drawing of cells.

Note that junctions are not yet covered but will be added real soon.

Also note that I changed "Saved File Specifications.md" into ["Whats-in-a-cell.md"](https://github.com/meisl/KNOH/blob/master/doc/Whats-in-a-cell.md)
...and have put both writings into the new folder `doc/`

TODO: update a few links here and related issues once this has been merged

TODO: delete this fork (make branches instead) once this has been merged