Added todo note
gravmag.tesseroid now faster than C Tesseroids thanks to replacing list building in _need_divide with numpy fancy indexing and conditionals
Added module for gravity effect of half a spherical shell
Added unit test for tesseroid potential. failing
Added half shell module import to gravmag init
Corrected bug in gravmag.tensor.center_of_mass when using 1 window
Fixed failing test for tesseroid. Was using too large shell model
Added more tests to tesseroid. Passing
Removed cython extension for distance in tesseroids. numpy version is faster
Updated benchmarks for tesseroid