Update setup.py PROJ version checking

[micahcochran]

In check_proj_version() add installed PROJ version to error message, return proj_version, use pkg_resources.parse_version() to provide a more featureful Version object.

After @snowman2 asked about the matter, so I just dug into it. This is the better Version object because distutils LooseVersion and StrictVersion are poorly documented and support the superceeded PEP 386. pkg_resources.parse_version follows PEP 440, and pkg_resources is provided by setuptools.

The returned proj_version value could be useful if there needs to be some other steps that have to be taken for future version of PROJ, while supporting older PROJ versions with operators such as
version >= parse_version('6.1.0').

So on my system it provides this error message

micah@micah-laptop:~/prj3/pyproj$ pip3 install .
Processing /home/micah/prj3/pyproj
    Complete output from command python setup.py egg_info:
    ERROR: Minimum supported proj version is 6.0.0, installed version is 4.9.3.
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-o3a25tgo-build/

[snowman2]

This is a nice addition! Side note: I wasn't referring to the setup.py in my previous comment, but this seems to be a beneficial miscommunication. I probably should have communicated that better. Originally thinking about test coverage for checking the pyproj.proj_version_str was set properly.

[snowman2]

Approved from my end.