Add a function to query the underlying transport type. This allows the
dive computer backends to implement transport specific behaviour where
necessary.
For the built-in I/O implementations, the transport type is obviously
always hardcoded, but for a custom I/O implementation the application
needs to provide the correct type. Hence the transport type can't be
hardcoded in the vtable and needs to be passed as a parameter.
With the new interface, an application can easily retrieve the
underlying transport type from the device descriptors and present a
custom user interface element to the end-user for supplying transport
specific parameters. For example the serial port for devices using
serial communcication.
For devices using a usb-serial chipset or the bluetooth Serial Port
Profile (SPP/rfcomm), the transport type is DC_TRANSPORT_SERIAL, because
internally the serial emulation layer is used for the communication.
Applications can now enumerate all the supported devices at runtime,
and don't have to maintain their own list anymore. The internal list
does include only those devices that have been confirmed to work at
least once without any major problems.
As the name already indicates, a device descriptor is lightweight
object which describes a single device. Currently, the api supports
getting the device name (vendor and product) and model number. But
this can extended with other features when necessary.
