Updated kernel.unload to support new kernel data model, code cleanup
Some code cleanup with pylint
Changed imports to be relative
Code cleanup and added 'center' argument to extra.angle()
Code cleanup and changed kernel.load to return all parsed objects
Added parsing for text (tf, tpc) kernels
Updated tutorial and documentation
* Added links to official spice documentation
* Added passage about bodies and reference frames
Fixed problems in kernel.py and bodies.py
* Sun now has its own class
* fixed parsing of .tsp files
* other small stuff