This commit should start to allow some Prolific PL2303 devices to work.
Tis device has a rather more complex initialization process than some
of the other devices.

I have tested this some with one device that I used to use to program
some older RS232 based boards plus talk to an SSC-32 device.
Test case is I am able to talk to SSC-32 and if I type in ver<cr>
It does properly return the version number.

The data I am seeing is pretty close to what
was documented in: https://gist.github.com/tommie/89011c5ac06553d5cdb8
as well as what the Linux driver outputs.

I also incorperated Frank's configuration options.

Have some support in place for the CDCACM serial class code.

It appears to be working for talking to a
Teensy that is programmed USB=Serial
or USB=Serial+...

Also test with an USB2AX board which is a Servo controller for Dynamixel servos (AX-12), that is an Atmega32u2 board programmed using LUFA as the USB library.