Dithered image combination for Python

 The drizzle library is a Python package for combining dithered images
 into a single image. This library is derived from code used in
 drizzlepac. Like drizzlepac, most of the code is implemented in the C
 language. The biggest change from drizzlepac is that this code passes
 an array that maps the input to output image into the C code, while
 the drizzlepac code computes the mapping by using a Python
 callback. Switching to using an array allowed the code to be greatly
 simplified.