FIX: Added importlib as a requirement according to Pull Request #30.

Just added this "manually" to cut it short because the Pull Request had a conflict.
See https://bitbucket.org/wradlib/wradlib/pull-request/30/importlib-missing-in-requirementstxt
for details.

Entirely removing BUFR support from wradlib.

Affects modules bufr and io, the documentation, the examples and examples/data.

Our policys from now on should be to refer users to the OPERA software webpage
at http://www.eumetnet.eu/opera-software (see tutorial_supported_formats.rst)....

DOC: some minor additions and changes

Added build scripts for CI

--HG--
branch : /feature/tp/ci

MIN: changed some phrases in the 'known issue' section

FIX: rscale,ascale

--HG--
branch : feature/eg/gabella_polar

NEW: test_filter_gabella_a_polar ENH:filter_setup

--HG--
branch : feature/eg/gabella_polar

NEW: clutter.filter_gabella_polar

--HG--
branch : feature/eg/gabella_polar

DOC: changed Section Title from `Installation Problems` to "Known Issues"

DOC: added `Installation Problems` section under gettingstarted

README.md edited online with Bitbucket

Merged in heisterm/wradlib (pull request #32)

FIX: Make testrunner return exit code 1 in case of failures.

MIN: PEP8 cleanup and reformatting of Rainbow IO Functions

MIN: PEP8 cleanup and reformatting of Rainbow Test Functions

MIN: changed example filename and added header, changed reference to example file in DOC

DOC: added Gematronik Rainbow section in supported radar formats

MIN: removed original GEMATRONIK rainbow classes

ENH: added xmltodict to requirements, added xmltodict as optional dependency in getting started doc, minor changes in test_io.py and io.py regarding xmltodict import

ENH: added example for reading and displaying rainbow format example file

ENH: added rainbow format example file from single pol rainscanner (operated by FZ Juelich), minor change in test_io.py