How do I send part of an ArrayBuffer to SPI

So why not add lcd_spi_unbuf_drawImage

I probably wouldn't want to merge something in if it was a specific hack for drawImagejust for lcd_spi_unbuf.c.

There are some really easy wins for lcd_spi_unbuf.c speed though. Something like:

int lastx,lasty;

void lcd_spi_unbuf_setPixel(JsGraphics *gfx, int x, int y, unsigned int col) {
  uint16_t color =   (col>>8) | (col<<8); 
  jshPinSetValue(_pin_cs, 0);
  if (x!=lastx+1 || y!=lasty) {
    disp_spi_transfer_addrwin(x, y, LCD_WIDTH, y+1);  
    lastx = x;
    lasty = y;
  } else lastx++; 
  spi_data((uint8_t *)&color, 2);
  jshPinSetValue(_pin_cs, 1);
}