birdtechstep

@hzeller chip select (cs pin) active low

@hzeller My friend dev. on stm32 said SetBits strobe hi on columns_-4 (led_width-4)

add lib/framebuffer.cc (line 587 ) work. ``` edit 582 for (int col = 0; col < columns_; ++col) { 583 const gpio_bits_t &out = *row_data++; 584 io->WriteMaskedBits(out, color_clk_mask); // col...