Ensure that downsample.pyx preserves image flux
Added cython compiler directives and array index cleanup in downsample.pyx
Added upsample cython function
Import util functions into top-level utils namespace
Import cython code in try...except block
Merge pull request #72 from larrybradley/utils

Added upsample cython function; fixes to downsample function to preserve image flux
Fix upsample for factors > 2