New release 0.5.1 using IPhreeqc 3.7

[Dr. Mike Mueller]

Hi PhreeqPy users,

I just released a new version of PhreeqPy.

Please install with:

pip install -U phreeqpy

The main changes are:

* Updated documentation to PHREEQC3
* Added IPhreeqc 3.7.3 and mac arm64 (M1) version
* Added parallel example

Let me now if you have any problems with the new version.

Best,
Mike