Updated GHCN_stations script to:

1) draw station location information from postgres database and perform merge/join query within database rather than r
2) add function to buffer region of interest to include stations outside region (to minimize edge effects)

Merging with bp/interp to use some of Benoit's code for precip interpolation

Merge branch 'bp/interp' into aw/precip

OR data preparation, initial commit for extraction of covariates from raster stack

OR data preparation task#363, modified code for ghcn to create a shapefile

GHNCD station data selection using Postgres database, initial commit, task #363

GAM LST, added specific and general diagnostic measures (e.g.MAE) GAM+Kriging, task #364 and #406

GAM LST, adding lines to summarize samling RMSE using plots, task #409

GAM LST, first code to test effect of sampling on GAM, task #409

GAM LST, added model and modified summary plots, run on 365 dates GAM+Kriging, task #364 and #406