FIX: check for GEOS enabled GDAL in examples zonalstats

FIX: check for GEOS enabled GDAL in test_zonalstats.py

DOC: change bleeding edge section in release_notes.rst

ENH: make wradlib/docs/source *.rst files python2/3 compatible

ENH: make wradlib/doc/source/pyplots scripts python2/3 compatible, reformat code, revise docstrings

ENH: make sphinx use `napoleon` extension for imporved docstring handling

ENH: make wradlib/examples python2/3 compatible, reformat code, revise docstrings

ENH: make wradlib/wradlib/tests python2/3 compatible, reformat code, revise docstrings

ENH: make wradlib/wradlib python2/3 compatible, reformat code, revise docstrings

ENH: make setup.py and testrunner.py python2/3 compatible

Merged wradlib/wradlib into default

Added tag v0.7.0 for changeset 26b592e80343

MAINT: Set version from 0_6_0 to 0_7_0 and updated release notes accordingly.

ENH: use latest gdal/ogr enhancement (prepared_containment test) to further speed up layer intersection

ENH: add `get_geom_properties` in DataSource class, make ZonalDataBase class and derivates calculate index and weights instantaneously

DOC: add tutorial for zonalstats module

DOC: correct bullet list alignment in docstring

ENH: make ZonalStatsBase and subclasses work with precalculated ix and w without the immediate need of ZonalData

MIN: move `SetProjection` before RasterizeLayer to get correct Proj output

DOC: add DataSource class docstring