Support for compatible release operator ~=

[y0m1g]

Hello,

I've noticed pur does not support the compatible release operator, i.e. ~=.
As described PEP-0440, ~= 1.4.5 is equivalent to >= 1.4.5, == 1.4.* (https://www.python.org/dev/peps/pep-0440/#compatible-release), but even if pur is able to update from click >= 7.1.0, == 7.1.* to click >= 7.1.2, == 7.1.*, it does nothing with click ~= 7.1.0.
I suppose this would be the appropriate behaviour to implement in pur.

That being said, it wouldn't fit my personal use case: basically I'm usually "soft-pinning" my requirements, meaning specifying boto3 ~= 1.12.49 instead of using the == operator, to allow security patches and also avoid dependency hell when I'm using inter-dependent modules.
So in my case, using requirements with ~= operator, I would prefer pur to behave just like it does with the == operator, meaning updating to the latest available version.
Would there be a way to enable this behaviour somehow while staying PEP-0440 compliant?

Thanks.