DOC: Remove numpydoc from the Dependencies section in Getting Started.

We have a lot of dependencies now which are only related to building the docs.
numpydoc is only one of them. Instead, we should point to `requirements.txt` for
those who want to build the docs by themselves. I will do that under dev_setup.rst.

Merged default into feature/georef

--HG--
branch : feature/georef

DOC: min changes referring to correct function

FIX: changed hyperlinks for example files to correct wradlib-sources

FIX: changed unicode \degree presentation to pure ASCII because testrunner failed on codeship with an unicode error, some minor visualisation issues

MIN: changes resolving PEP-issues, fix unresolved string in `georef`

DOC: reworked PROJ.4 section in RADOLAN tutorial

ENH: switched :math: to use sphinx.ext.mathjax

DOC: minor fixes and changes in RADOLAN tutorial

MIN: removed default lonlat values from parameters in `get_radolan_coords`

MIN: added np.int32 dtype-value in test for correctly running tests in 32bit environment, as suggested by Maik Heistermann

MIN: added grids to plots, masked dots from RW and SF plots

MIN: changed function name to better represent capabilities, minor changes

ENH: added function `get_radolan_center` which calculates grid center coordinate, also added trig-keyword to toogle between standard trigonometric calculations and osr transformations, also refined grid setup

MIN: minor changes and fixes in example files

DOC: incorporated changes suggested by Maik Heistermann (colorbar with label, examples section, hyperlinks to example files, etc)

ENH: minor changes in `georef.get_radolan_grid` and test function, removing all the magic

ENH: minor changes in `georef.get_radolan_grid`

Merged default into feature/georef

--HG--
branch : feature/georef

ENH: added more test functions for testing `georef.get_radolan_grid` function