interpolate_points interpolates to top-left corner of pixel, not center

[emlys]

The wind energy model expects that interpolate_points interpolates values to the center of each pixel.
The coordinates passed to scipy.interpolate.griddata are the upper left coordinates of each pixel:

pygeoprocessing/src/pygeoprocessing/geoprocessing.py

Lines 1127 to 1140 in ff5eb8e

	for offset in offset_list:
	grid_y, grid_x = numpy.mgrid[
	offset['yoff']:offset['yoff']+offset['win_ysize'],
	offset['xoff']:offset['xoff']+offset['win_xsize']]
	grid_y = grid_y * geotransform[5] + geotransform[3]
	grid_x = grid_x * geotransform[1] + geotransform[0]
	# this is to be consistent with GDAL 2.0's change of 'nearest' to
	# 'near' for an interpolation scheme that SciPy did not change.
	if interpolation_mode == 'near':
	interpolation_mode = 'nearest'
	raster_out_array = scipy.interpolate.griddata(
	point_array, value_array, (grid_y, grid_x), interpolation_mode,
	nodata)