Reading grid information from WRF files

The module emiprep.wrfgrid will handles calculations regarding the WRF horizontal gridding.

In order to do the spatial remapping of emissions to the WRF grid, we need information on the extents of the grid cells. By default, the wrfinput_d0X files only contain the grid cell centers (in the variables XLAT and XLONG). Information on the corners can be obtained in two ways:

1. Reading geogrid output files in addition to wrfinput_d0X (there, the grid cell corners are contained in the variables XLAT_C and XLONG_C.)
2. Modify the WRF registriy so that XLAT_C and XLONG_C are contained in the wrfinput_d0X files.