Mostly doc string tweaks for graph classes, tutorial.
Fixes of blockmodel and antigraph examples
api_changes and release_2.0 updates.

When data=True, the whole data dictionary is returned for each edge.
When data=False, no data is returned.
Otherwise data is used as the attribute name of the edge data to return.
>>> [ (u,v,edata['weight']) for u,v,edata in G.edges(data=True) ]
becomes
>>> G.edges(data='weight')

>>> for n,nbrs in G.adjacency_iter():
...     for nbr,ddict in nbrs.items():
...         print (n,nbr,ddict.get('weight',1))
becomes
>>> G.edges(data='weight', default=1)

This reverts commit e736d4b4db44f45c59039d44f92013748cbef3f4, reversing
changes made to ceb31d0f4f14556d4e804868efd23c11f2e6b776.

Drawing with pydot/Graphviz and inline IPython displays.