Separating out RegRectilinearGrid dispatch #108
Description
When the code was originally written, it was written for a RegRectilinearGrid. This means that many equations that depend on the grid, simply use RegRectilinearGrid fields and do calculations assuming a regular rectilinear grid.
If a user wanted a new grid type, they would need to look through the coupling code and pull out the code that depends on the grid being regular rectilinear and put this in helper methods that dispatch off of the grid type. The user could then write their own methods fo their new grid type that dispatch off of these helper functions.