Simple graphics library

Will draw Adafruit GFX compatible fonts, lines, squares, and it will also fill a square. It can draw or clear any of these. That's it, graphics as God intended.

Made for ST7920 with my own driver library, but it should be pretty universal, it just needs draw and clear functions taking x,y coords of a pixel + some user context.

The API is pretty self-explanatory, but just in case

const gfx_canvas_t canvas = {
	.ctx = &dev,
	.draw_pixel_callback = st7567_draw_pixel,
	.clear_pixel_callback = st7567_clear_pixel,
};

const GFXfont *font = &FreeSans9pt7b;
st7567_clear(canvas.ctx);
gfx_fill_box(&canvas, 40, 40, 8, 8, false);
gfx_draw_string(&canvas, font, 0, 16, "Hello", false);
st7567_update_screen(canvas.ctx);

Would be good to add a functionality to draw some bitmaps and some included default fonts. Cozette, Spleen, Terminus, those tiny ones from JP guy