Create unit tests

[ehermes]

Sella currently has no unit tests, as up to this point, the interface has been somewhat in flux.

We intend on stabilizing the current interface. Therefore, we should write unit tests.

What follows is a potentially incomplete list of functionality within Sella that could benefit from unit tests.

• Full saddle point refinement
• Full minimization
• Optimization with constraints
• Constraint initialization
• Trust radius update
• RS-P-RFO step determination
• Iterative eigensolver
• Approximate Hessian updates
• Orthogonalization procedures
• Y matrix symmetrization

There are also some features within Sella that are currently broken or not being used. We may want to write unit tests for these features as well.

• Intrinsic Reaction Coordinate (IRC) optimization
• Internal coordinate construction
• Cartesian -> Internal transformation
• Internal -> Cartesian transformation
• Hessian Internal/Cartesian transformation
• Force-field force matching

Unit test contributions are welcome.