Add support for absolute paths

[Neme]

On Windows, attempting to open a serial port using a Device Interface Path instead of a traditional COMx port name results in a failure.

For instance: trying to open \\?\USB#VID_0483&PID_5740#158133603236#{86e0d1e0-8089-11d0-9ce4-08003e301f73} will fail.

Fixes: #258

[sirhcel]

Thank you for spotting this issue and opening a PR @Neme! It looks good and giving it a spin with a SiLabs CP2102N and transmit.rs works like a treat:

> cargo run --example transmit "\\?\USB#VID_10C4&PID_EA60#YOUR_SERIAL_NUMBER_HERE#{A2A39220-39F4-4b88-AECB-3D86A35DC748}" 115200

I'm using the interface GUID from Windows USB Device Path here.

[Neme]

@sirhcel I noticed that the x86_64-pc-windows-gnu / build job failed. Do you think this is related to my changes, or could it be a CI/environment issue?

[sirhcel]

I assume the failed CI build for x86_64-pc-windows-gnu being completely unrelated to your change (as it does in this build for #260 as well). Do you have an idea of what's going on there? I tried to reproduce this issue locally but did not succeed yet.

[surban]

Might be a 32-bit DLL in PATH before 64-bit DLL of Mingw.

[sirhcel]

Let's ignore the CI issue for now and integrate this change. I can't add a changelog to your branch @Neme (presumably because it is in the repo of an organization an not an individual). Could you please cherry-pick the changelog sirhcel@627f684?