Add ability to specify explicit margin sizes to graphs.
Add ability to specify explicit margin sizes to graphs.

Set the defaults so that reasonable values fit. Allow applications to
configure any combination of margins explicitly by using separate
fields.

pignacio/python-nvd3,liang42hao/python-nvd3,yelster/python-nvd3,BibMartin/python-nvd3,yelster/python-nvd3,Coxious/python-nvd3,oz123/python-nvd3,pignacio/python-nvd3,vdloo/python-nvd3,mgx2/python-nvd3,yelster/python-nvd3,BibMartin/python-nvd3,Coxious/python-nvd3,oz123/python-nvd3,vdloo/python-nvd3,Coxious/python-nvd3,vdloo/python-nvd3,liang42hao/python-nvd3,pignacio/python-nvd3,mgx2/python-nvd3,BibMartin/python-nvd3,oz123/python-nvd3,mgx2/python-nvd3,liang42hao/python-nvd3