Add 1-Wire support to FT232H via GPIO

[TuxInvader]

This change adds a OneWireDevice class to the FT232H module and enables support for 1-wire devices via GPIO bit-banging.

Rather than attempt to handle the 1-wire timings directly in python (and at the mercy of the kernel scheduler), we write command pipelines to the MPSSE, and it handles the high low transitions to perform RESET, WRITE-1, WRITE-0, and READ.

The code includes the option for 1-wire "overdrive" speeds, but I have not tested this personally. I'm using this code to talk to a digital thermometer (DS18b20) which only supports standard mode timings.

The GPIO pin used for 1-wire needs to have a pull-up resistor to the 5v line. I used a 4k7. 1-Wire devices can operate in parasite power mode where they charge themselves directly from the data line. I have tested both powered and parasite modes with my thermometer.

[ladyada]

hiya thank you for the pull request. we're going to be deprecating this library in favor of our python3 Blinka library which has support for almost 200 different drivers, and a wide variety of linux computers as well as ft232h