User Controlled Maximum Grid Sizes

[hatfullr]

We need to give the user control of the maximum grid sizes allowed in flux_cal. Some users may have situations where they need a very high resolution, or perhaps a very low resolution, and we wouldn't want to make them go into the code and edit a parameter value haphazardly.

[hatfullr]

This will require careful implementation of the "allocate" builtin function staged at the beginning of init.f.

[hatfullr]

This may be difficult to implement because allocatable arrays cannot be placed in common blocks. We would need to pass the required arrays to each subroutine that needs them. To do this, we would need to place each subroutine into a module, as per this Stackoverflow answer.

For now, I have added some user controls for the minimum and maximum resolution in the x and y directions for the driving grid.