First crack at fixing multiple links

* Makes MultiGraph more like networkx.multigraph
* Adds converTo method
* Synchronizes node1 with xxx1 in link options
Allow natural sort to accept non-strings.
Allow Mininet() to accept multi-link topos w/correct params.
add example and test for multiple links
Minor fixes
Return (src, dst) in original order, and allow keys + data
Remove unused edgeinfo
Fix edges() and add convertTo() to Topo() (with keys option)
Ignore link info when sorting links.
Remove unnecessary 0
Get rid of paramDict and simplify things a bit
Make port1, port2 truly optional and don't pass them to Link()
Add a few clarifying comments
Merge pull request #416 from mininet/devel/multitopo

Multi-link topology support