The poweroff() and poweron() methods are used to do soft power control of
the display, and this patch makes these methods work the same for both I2C
and SPI interfaces.
It removes the need for a wrapper Python function to dispatch to the
framebuf method which makes each function call a bit faster, roughly 2.5x.
This patch also adds the rest of the framebuf methods to the SSD class.
In particular, the WeMOS D1 Mini board comes with a shield that has a
64x48 OLED display. This patch makes it display properly, with the upper
left pixel being at (0, 0) and not (32, 0).
I tried to do this with the configuration commands, but there doesn't
seem to be a command that would set the column offset (there is one for
the line offset, though).
