[WIP] Fix to ppm chemical shift wrapper, better tests, CI integration.

But their shebang line is `#!/usr/bin/env python`.  And as far as I can tell, the install process doesn't use `distutils` (which I believe replaces the shebang line to use the interpreter used to build the package in the first place).  So I think you'd have to assume that the shebang line would just be the first `python` you can find in `PATH`.

Using `python2 shiftx2.py` would allow us to ignore the existing shebang line and forcibly use the interpreter we want to use for it.