Bug fix in gravmag.prism: wasnt importing cython modules because of typo
Removed unused variables in cython gravmag.prism
Removed import in constructor of Data in gravmag.harvester
Added upload to pypi to makefile and removed out of data harvester script
Added test for gravmag.polyprism comparing with gravmag.prism
Made gridder.cut return a slice of the arrays instead of a copy