Changes necessary to compile on arch linux (py38)

[cassfalg]

I've made some necessary changes to compile pptk and create a wheel file for me on Arch Linux with Python 3.8. This solves both #37 and #39. I have tried to ignore the Windows and Apple sections and leave them mostly alone, but I would not expect this to work on those platforms without more modifications. Hopefully someone can expand my work and address those issues.

Here is the wheel file for convenience:
pptk-0.1.1-cp38-none-manylinux2014_x86_64.zip

To solve issue #39:

Removed old Find*.cmake files to use the ones provided by the
system packages, and made necessary changes to multiple
CMakeLists.txt to use those. Switched to imported targets.

Changed imports of numpy heders in cpp files to be compatible with the
folder structure provided by system packages.

To solve #37:

Modified setup.py to be compatible with pip 20.

Feedback would be appreciated, especially if this compiles on other systems. @victoriousluser I hope you can use this to add a wheel file to PyPI?

[kamiccolo]

Is there a reason You have bumped the minimum required CMake version?

[cassfalg]

Yes. Is that a problem for you? Can you try what fails and offer alternatives?

The FindPython module requires 3.12 according to the docs, and something else (don't remember atm) required 3.14 so I put that everywhere. It is not necessary everywhere and I have not tested or tried to push it down. I don't really want to either.

[kamiccolo]

Yup, You're right. Just trying to be careful with those bumps :} Not every distro has this fast pace with package versions...

Can't build pptk anyways :D

[kentaroy47]

Nice, hope that this will be merged and whl would be updated..

[yosefm]

Hi all. Are there plans to merge this? We're all holding back on upgrading our Python version here, due to pptk. Thanks.

[ThorJonsson]

Same here for me in 2022.

[nikste]

thanks for this PR!