and gpio slowdown values.
o Add gpio slowdown to the values that can be modified programmatically
and with flags.
o Have the default flags passed into CreateMatrixFromFlags() also be
an output value, so that the settings read from the flags can be
used back in the user program.
o Allow to set show-refresh-rate, inverse-colors and green-blue
swap programmatically. That way, nobody has to re-compile just for
these options, which makes things more easy to distribute as library.
also: Make these flags.
