Switched to using BytesIO rather than StringIO for importing data from URL to numpy

Dealt with changes in module locations for urlopen

Further fixes for py6s. 2to3 now suggests no further changes to files.

Update to make it work with python3. This translate was done by Dan Clewley, working to finish it off.

Added BibTeX to CITATION

Added CITATION file

Update installation with typos from Ted

Added exception handling for 6S output parsing

Merge branch 'master' of github.com:robintw/Py6S

Fixed bug where geometry parameters were only being specified as ints.

Added more detailed error messages for failures during AERONET data import.

Added test for the changing altitudes bug.

Made AOT argument to custom altitude function optional.

Fixed bug where changing sensor altitudes to satellite or sea level fails after custom altitude set

Updated docs, particularly for run_wavelengths using arange etc