This patch adds a ftdi_bb programmer type. Unlike the ft245r driver, this one
does all the heavy lifting through bitbang.c and hence supports TPI. It can
be built both using libftdi1 or FTDI's FTD2XX library (which seems to be much
easier to install on Windows).
On Linux, a 1KiB flash can be written in about 3 seconds. Windows seems to be
about 10 times slower.