Replace pkg_resources with packaging/importlib

[jonpas]

Fix #71

Some Python and package version requirements should probably be changed with this, it's essentially the first step to moving to newer packaging solutions for Python.

[sleeptightAnsiC]

Thanks. Out of curiosity: does it make it possible to run ue4cli with the Python implementation that ships with Unreal Engine? If I remember right, this was the reason why I was trying to remove those dependencies in the first place.

[jonpas]

I am not sure, but very possible as I assume Unreal ships newer Python version. I have never used Python shipped with Unreal before, if there is an easy way to test that, I can give it a shot.

[sleeptightAnsiC]

if there is an easy way to test that, I can give it a shot

the Python executable should be somewhere under: [unrealengine]/Engine/Binaries/ThirdParty/Python3/[platform]/

but I think you may have a problem with invoking ue4cli directly due to #70

[jonpas]

Testing in a Linux Unreal container:

$ cd ~/UnrealEngine/Engine/Binaries/ThirdParty/Python3/Linux/bin
$ git clone https://github.com/jonpas/ue4cli
$ ./python3 -m pip install -e ue4cli/
$ ./ue4 version
Using user-specified engine root: /home/ue4/UnrealEngine
5.5.4

Seems to work fine. 🎉

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You shouldn't need #70 with pip install -e. ue4cli should be installed, I don't think it was ever meant to be ran directly as a script.