add python notebook demo + minor bug in logging

 Changes to be committed:
	new file:   doc/ecospold2matrix_demo.ipynb
	modified:   ecospold2matrix.py
Update README to point to demo

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 Changes to be committed:
	modified:   README.md
More update on README: open source + change subtitles

 Changes to be committed:
	modified:   README.md
mention re-use of code from brightway2 and link to it.

 On branch master
 Your branch is up-to-date with 'origin/master'.

 Changes to be committed:
	modified:   README.md