This creates a testable framework so that we can easily test order of convergence on things like operators by just writing the guts of the code.
Merged Seogi's code into this framework.
This is under the DiffOperators class, which can be inherited with BaseMesh to any Mesh Object.
Cell area and other dimension calculations are included in the TensorMesh class.
Wrote unit tests for cell vol, area, and edges.
Rowan Cockett