Dev.Clear: Avoid writing one beyond the end of the line. Also build the
row data only once before sending it for each line.
Dev.Draw, Dev.DrawPartial: Deduplicate logic for iterating over pixels
and simplify it such that a whole row of bits is built before sending
them in one go.
Tested using a Waveshare e-Paper 2.13in V2 display.
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
hansmi