Merge pull request #32 from ralphbean/master

Clarify License
Fix empty bottom legend
Merge branch 'master' of github.com:Kozea/pygal
Avoid empty interpolation crash
Add worldmap chart
Work on worldmap, better svg + new data definition
Fix a lot of things in Worldmap
Support multi title in worldmap
Fix range
Fix empty interpolation and add tests for it
Add missing svg Fix #33
Start a compat module
Bump copyright
Same code for python 2.7 and 3.3
Consequently fix tox.ini
Fix unicode litterals
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-_-
Wrap forgotten u''
Add test for unicode in labels for python2/3. References #16