started documenting driver circuits and control logic
added driver diagram

Created a diagram of a single sprinkler driver circuit.
It was drawn using Inkscape.  And the output format is suited
for LaTeX so that the fonts look nicer and special symbols
can be used (e.g. $\Omega$).
switched to Inkscape without LaTeX

The LaTeX output with Inkscape was neat since
LaTeX formatting characters could be used.  But
the placement and the font size was different
than the diagram.  The result is easier to control
using the fonts in the diagram are used.
changed solenoid icon from curlys to humps
documented power supply

Documented the major components of the power supply
(transformer, rectifier, 7805).  Also included
a circuit diagram drawn with Inkscape.
added control diagram

A diagram of the control circuit has been added.
It includes the SPI to shift register and decoder logic.
updated +plus link in README
general doc cleanup, moved figs/ to svg/

Renamed figs/ to svg/ since these are all Inkscape
diagrams in .svg format.

Cleaned up the SPI message format diagram by using a
table instead of verbatim text.