global: license header and PEP8

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
global: Python 3.3+ support

* Adds PY2/PY3 compatibility layer.  (closes #2)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
docs: initial draft

* Adds new Sphinx documentation page.  (closes #3)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
contrib: new spires module
visitor: simple inheritance addition
spires: separation to contrib module

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>