Currently the `FrameBuffer.blit(buf, x, y)` method requires the `buf`
argument to be another `FrameBuffer`, which is quite restrictive because it
doesn't allow blit'ing read-only memory/data.
This commit extends `blit()` to allow the `buf` argument to be a tuple or
list of the form:
(buffer, width, height, format[, stride])
where `buffer` can be anything with the buffer protocol and may be
read-only, eg `bytes`.
Also, the palette argument to `blit()` may be of the same form.
The form of this tuple/list was chosen to be the same as the signature of
the `FrameBuffer` constructor (that saves quite a bit of code size doing it
that way).
Signed-off-by: Damien George <damien@micropython.org>
