Move comments from samp core.py to __init__.py
Move extensive example to sphinx docs; minor cleanup
Remove unused includes
Rename astropy.vo.samp.core to astropy.vo.samp.utils
Break up astropy.vo.samp into multiple files.

This was discussed and agreed on in GH #972.
In addition to the structure suggested there by @lpaioro,
I put the constants and errors in separate files.
Remove import * in vo.samp ... now imports are fixed for Python 3
Fix docstring parsing error in vo.samp with Python 3
Simplify Python 2 / 3 imports a bit by using the six compat module
Manually convert all vo.samp docstrings from epydoc to numpydoc format
Run autopep8 to clean up all astropy.vo.samp code

cd astropy/vo/samp
autopep8 -i --ignore E501,E126,E128,E225,E226,E231 -r . tests/