Change type of mask to int8_t

src/Longinfo.cc

src/Remapgrid.cc

src/Remapweights.cc

src/Timstat.cc

src/Trend.cc

src/knn_weights.h

src/remap.h

src/remap_bicubic.cc

src/remap_bilinear.cc

src/remap_conserv.cc

src/remap_distwgt.cc

src/remap_scrip_io.cc

src/remaplib.cc