Incorporate EOF analysis

[gutmann]

Downscaling often uses a PC time series of EOFs computed over a larger spatial domain. It would be nice to let GARD pre-process a given variable (e.g. sea-level pressure) to compute EOFs and corresponding eigenvector weights.

[gutmann]

This could incorporate David Pierce's EOF Fortran library
http://meteora.ucsd.edu/~pierce/eof/eofs.html