Numpy 1.5 is fine, no need for 1.6

Relaxed the numpy version dependency because OSGEO4W currently has 1.5
packaged.
Installation instructions for Windows
Transform station co-ordinates before spatial integration

create_ogr_layer_from_stations now receives an integer epsg argument
and converts the stations co-ordinates from WGS84 to the co-ordinate
system specified by epsg. (Prior to this, bitia's calculations were
totally wrong because the study area's co-ordinate reference system was
defined nowhere.)