add pd Vendor messages and badge detection

[ChrisDick]

Description

Cleaned up the stack and added host and device vendor messages to pd. This allows users to send and receive vendor messages on both ports once USB attach is complete for that port.

If a device is attached to a host port a vendor message is sent. If message is received by the badge on the usb in, it detects the other badge and connects as a device, it responds with the same message to let the other badge know it is connected as a host.

includes a helper to construct a vendor header and events to signal a badge has been connected and messages received.

It also contains code for prime and double prime messages, but there is an issue with the packet creation and the end of packet symbol is being inserted by the fusb302 before it stuffs the CRC in the packet. hopefully this will be enabled in a future PR.

[Jonty]

This is EXTREMELY COOL

[ChrisDick]

I've changed this to draft as I've started doing the docs and want to improve the mp api, it's a bit verbose and could do with being split into host and device classes and improving the connection status getters.

[ChrisDick]

updated the api to the following, using separate classes as host may be extended with prime messages, which a device deosn't send:

>>> from pd import Device, Host
>>> dir(Device)
['__class__', '__name__', '__bases__', '__dict__', 'badge_connected', 'connected', 'get_vendor_msg', 'pd_enabled', 'send_vendor_msg']
>>> dir(Host)
['__class__', '__name__', '__bases__', '__dict__', 'badge_connected', 'connected', 'get_vendor_msg', 'pd_enabled', 'send_vendor_msg']

[ChrisDick]

going to make further improvements to the api