mqtt monochrome blit to oled

[neonsignal]

updated version of MQTT command to send a monochrome image
replaces pull request #31

(oled:blitm x y width height base64_data)

x,y is the destination screen location; if x is greater than the first screen width, it will offset to the next screen and so on, but will only be placed onto a single screen

width,height is the width and height in pixels

base64_data is the image encoded as a bitmap, horizontal scanlines, high bit first, and then converted to base64 with padding; because there are 8 pixels per byte, the image must be a multiple of 8 pixels wide

The image to be sent must be converted to a base64 encoded string with proper padding. The blit location is specified by x,y (if x > screen width, it will place the image on a subsequent screen).

example
(oled:blitm 32 0 48 64 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)

[garthk]

Fits right in with the existing design.