Don't abort in date2stamp or stamp2date when invalid dates/stamps are provided.
Started implementing lat/lon extraction for each grid type.

Note: this code will be removed, in favour of using the built-in grid support
from rmnlib.
Implement a get_latlon function (in C extension) to compute the latitude/longitude values.

Uses the EZSCINT module of rmnlib to do the calculations, so it should handle
any model grid.
Check if lat/lon arrays can be reduced to 1 dimension.

Also, minor bug fix in the dimensioning of the arrays.
Remove old Python code for generating lat/lon grids.

This is handled in the extension module and rmnlib.
Include x/y coords when returning the lat/lon arrays.

Also, disable support for 'Y' grids.  Extra logic would be required to handle
the dimensioning of the coordinates, and I have no sample files available.
Attach lat/lon axes to the variables.
Store any auxiliary 2D lat/lon fields that the variables may need.