Create radial Jastrow functors from symbolic expressions

[markdewing]

Generate code for a radial Jastrow functor from a symbolic expression.
The template is UserFunctor.h.in and the user_jastrow.py script fills it in.

The output of the script also includes sample XML input.

This commit removed a number of Jastrow forms.
df44e6b

The script is a way to easily recreate various forms without needing to store much code.

An existing UserFunctor.h is already present (corresponding to a simple Pade form) for compilation.

[PDoakORNL]

So this is very cool, but where are unit tests?

[markdewing]

I'm uncertain how to create a reliable unit test. The test will need to assign some values to the parameters. One option is require users to assign some reasonable values or specify ranges in the script.

[markdewing]

Updates include a unit test. It will require changes to test new functional forms, but at least the basic test is there - it should not be too hard to modify. In the future, the code generation step output some of the changes needed for the unit test.

[prckent]

Test this please

[PDoakORNL]

It is excellent to have a C++ unit test.
But I was also thinking about the python itself:
i.e. https://docs.python.org/2/library/unittest.html
Looking around the project we don't actually do any testing of python code itself.
So this is probably a discussion to have after this is merged.
But since this python code produces output that is pretty crucial this wouldn't be a bad place to start.