upgrade PyQt build

[luelista]

Hi,
I'm working on upgrading the build process of the PyQt bindings to the current recommendations of the PyQt-builder / sip authors, so that it works with the current version of sip and pip.

It's currently WIP because I can't build the resources file (ads.qrc) reliably yet. It only works if the build directory is in a subfolder of the main repo, because I had to hardcode the path in the config file (qmake-settings = ["RESOURCES += ../../src/ads.qrc"].

Once I found out the right way to solve this I'll update this PR. I thought I'd still open this already, if you have any feedback regarding this update.

[githubuser0xFFFF]

Thank you for your contribution. I cannot help you much, because I have not experience yet with PyQt. Just tell me when you think the pull request is ready and I will merge it.

[luelista]

I fixed the build problem, no hardcoded path any more :) I'm going to test this on some more platforms, and tell you once it's ready.

[githubuser0xFFFF]

This sounds great. Thank you very much for your help.

[Zholtikov]

@luelista Do I understand correctly that when you're done - there will be a PyPi package that can be installed with modern versions of pyqt-sip and pyqt ?
Can you tell me when you plan to finish? I really look forward to these changes...

[luelista]

@Zholtikov it is already possible to install, I put up a WIP version on PyPI: https://pypi.org/project/PyQtAds/
I compiled binary wheels for macOS, Linux and Windows.
Edit: Modern versions of PyQt5, yes - still no Qt 6 support

@githubuser0xFFFF
I tested it on macOS, Linux and Windows now, and also had some users test it. So I think this PR is ready now.

[githubuser0xFFFF]

Thank you very much for this great contribution,