good and fast resampling with scipy.ndimage

scipy.ndimage's interpolation methods are better than OpenCV's and faster than those in scipy.interpolate (which are for non-picture inputs), albeit slower than OpenCV's, so I've kept the choice but defaulted to scipy.ndimage

I've given the main script command line parameters and tidied it up a bit more

there's now a "picker" script that spares you from opening a photo editor and writing down line coordinates manually

initial release

release for citing purposes. made halfway presentable.