Pybufr-ecmwf

-move to library version bufrdc_000409
-make all code portable between python2 and python3 to remove the
need to run the 2to3 tool
-introduce travis testing for linux and MacOSX+Homebrew
-addition of a simple read interface in BUFRReader
(thanks to Christoph Paulik)
-reorganize documentation files
-addition of a first few lines to start building an interface
to the new ECMWF ecCodes library (still very experimental)

-license change to LGPLv3
-move to library version bufrdc_000403
-split download tool to its own file

-do no longer download the latest library version from ECMWF, to prevent
breakage in case they redesign their website or software package,
just use the packed tar file (the option to download can still be used though)
-updated to build and use the new BUFRDC series of the ECMWF library
including the latest versions 000400 and 000401.
-add reading, writing and using the C-BUFR tables which allows expanding
numerical flag values to the corresponding text values.
-fix a bug that happens if multiple bufr files using different templates
from different bufr table files are used in the same script.
-fase out the singletom trick since it made things too complicated
(and was only experimental anyway)

-fix pip install issue and add pip install test to build_test.py
-fix a whole bunch of new pylint warnings
(since pylint now also complains about whitespace)

-add a safety check to bufr_to_ascii.py and add a little sorting script
named sort_bufr_msgs.py, to prevent trouble in case bufr_to_ascii.py is
used on a file that contains mixed BUFR messages using different templates

-fix a mistake in the manifest file