Added same defaults to peek() as in map
Added some initial work towards animating MapCube using mpl.animate.

Also added sunpy.util.plotting which holds some of the more general animation
functions at the moment, but could be used for other general plotting routines.
Fixed having to have callbak in main script.
Add option for slider to plotting.add_controls
Moved sys_info to its own module.  Pulled imports out of function call.  Imported sys_info to util.
Moved unit conversion functions ('astronomy-type utilities, per schriste) to their own module.  Corrected __init__ so that the external interface doesn't change.
Cleaned up import of to_angstrom per the previous change to the location of the unit_conversions.  Removed unused to_angstrom import from __init__
Reordered imports per PEP 8
Added replacement_filename to the util namespace and cleaned up the imports throughout sunpy.
Added absolute_import to new files
Fixed for correct relative imports
Cleaned up import namespace for wcs module.  Made import sequence PEP 8 compliant.
Removed import of unused delta function
Removed delta from util.  It was only used in one place (spectrogram.py), where it obscured what was going on.  Additionally, spectrogram.py contained another line that had a similar delta operation, but was slightly different, so delta was not used there.  Delta was removed to make things consistent.
Corrected for change in util module layout
Cleaned up util imports
Finished cleanup of util's interaction with spectrogram.  min_delt was used as both a function call and a local variable in spectrogram and the function was never used outside, so the import of min_delt from util was replaced by the local definition of _min_delt.  This also serves to differentiate the function call from the variable name.
Finished cleanup of callisto's interface with sunpy.util.  Made callisto test import sequence PEP 8 compliant
PEP 8 discourages relative imports.
Finished cleanup of sunpy.util public interface