protocol.sfdp: mega→mebi

hardware: always download a specified bitstream if the header is all ones

platform.rev_c12: add connector definition for the lvds connector.

applet.interface.analyzer: fix pullup/pulldown polarity https://github.com/GlasgowEmbedded/glasgow/issues/271

doc: add details about libusb bug

examples: fixup PCF8574 usage

gateware.uart: fixup parity handling

Fix typos. NFC.

applet: fix simulation clock Argument to add_clock is a period, not a frequency. A very low frequency creates huge timestamps which overflows gtkwave.

applet.video.vga_output: convert to nmigen