Added fill_srtm and shade_srtm to srtm.py
osgeo is needed for filling the SRTM gaps.
Added an example to show how to get and shade an SRTM relief map
Added docstrings
renamed methods
updated example
clean import of gdal
added units (meters, km)
correction max_distance type=int and unit=pixel
bugfix max_distance
correted examples/srtm_shading_example.py
updated docs/source/whats_new.rst
typo
this should solve travis errors
actually, this one should
Added gdal in travis-ci configuration.