set_view no longer requires density.  arg removed.
	modified:   visualize.py
set_view takes no kwargs.
	modified:   visualize.py
Implemented cylindrical coordinate system.
	modified:   analyze.py
	modified:   hdf5.py
typo.
	modified:   analyze.py
Should not be messing w/units in orient_box()
	modified:   hdf5.py
Uniformly pass coordinates about as 3 by X array.
Force explicit conversion to individual coordinate arrays.
	modified:   visualize.py
use numpy.arctan2 to get quadrants right.
	modified:   analyze.py
Updated py_scalar_map inputs.
	modified:   visualize.py
Changed default number of centering particles.
	modified:   analyze.py
Only do simple centering if explicitly requested.
	modified:   hdf5.py
Bugfix: 'simple' centering --> 'box' centering.
	modified:   hdf5.py
Updated halo.radial_properties()
	modified:   halo.py
Cleanup after populating database.
	modified:   halo.py
Shell averaging corrected!
	modified:   halo.py
Added spherical/cylindrical coords to loadable keys.
	modified:   hdf5.py