Feature/net6 workaround

[TristanBoland]

It seems the QRCode Class is no longer available in QRCoder for .NET6.
Throws an "Could not load type 'QRCoder.QRCode' from assembly 'QRCoder, Version=1.4.3.0" exception currently.
I needed this library in one of my projects.
So i decided to publish my workaround to here. Hopefully it is of use to some

[ahwm]

@flytzen thoughts? I've been seeing more of these requests, not sure how we want to proceed.

[flytzen]

@flytzen thoughts? I've been seeing more of these requests, not sure how we want to proceed.

Well, if this works - which it looks like it does - then we should pull it in for now. We do need to test it on Linux, though. Even if it is "windows only", we can still do it as a short-term thing. I'll run the test suite on Linux.
But if codebude/QRCoder#315 isn't resolved soon, then I guess we will have to switch to a different QR coder library.

Relates to #100 and #98 and #94.
If we do switch to another lib then we probably want/need to drop legacy support (see #89) and only support netstandard2.0 up and bump the main version.

@TristanBoland Thank you!!

[flytzen]

@ahwm The tests are all passing on Linux as well, so I think we should merge this. I do want to just check a couple of things before we merge :)

[flytzen]

This is really great, thank you.
Minor suggestion to avoid duplication.
Slightly more important about adding the using statements to avoid resource leaking in high volume scenarios :)

[TristanBoland]

I accepted your changes, glad i could help! Was intended as a quick fix so i could go on with my Task, but glad it was of use

[flytzen]

@ahwm I'm approving this.
I'll do a separate PR with a new version number and a minor fix for a new warning in .Net 6.0.