/dev port unavailable on newer versions of MacOS

[rchtsang]

This isn't really a problem with the tool itself as much as it's a problem with drivers and confusion on macOS with new updates.

I'm using the CC3200 Launchpad, not a toniebox, so my use-case is probably different here,
but basically when I connect the launchpad, the device doesn't show up in the /dev directory, so I can't pass a /dev port to cc3200tool.

My fix (which I have not made into a PR, since I don't know if this is a common issue or if it fits the use case) is to use pyftdi as a backend for pyserial so that I can instead pass a custom ftdi url (ftdi://ti:launchpad:cc3101/2) to the cc3200tool to access the serial port directly as a usb device. I had to change the serial.Serial() instantiation into a factory function call to serial_for_url, which takes pretty much the same arguments, but better supports the device url format.

Just thought I'd leave this here in case anyone ran into a similar issue. And was interested.

To be clear, the cc3200 still showed up with lsusb with the name USB <-> JTAG/SWD device initially, there was just no corresponding /dev port open.

My fork is here.