Add sparse2adjacencylist

Perhaps the name is too long, feel free to change it.
Merge pull request #25 from dmbates/master

Add a sparse2adjacencylist function
Restore the missing comma from the last commit.
Merge pull request #27 from dmbates/master

Restore the missing comma
Adds recursive Tarjans.
Adds iterative version of tarjans.
Removes redundant anon. function usage.
Adds test for strongly connected components.
Merge pull request #29 from maxlikely/strongly-connected-components

Strongly connected components
update the behavior of show (show only shows a brief summary, and show_details shows more)
add .travis.yml
add DataStructures installation in Travis YML
Add Travis logo to readme
Starting random graphs
Fix a bug in building small world graphs
Fix the random tests and a bug in Watts-Strogatz graph generation.  They plot quite nicely now.
Sort of fix attribute modification in random graphs, this will fail unless attributes are removed from the Vertex hashing function.
Change to using test instead of assert, all broken right now.
Fix small mistake in graphs.rst
Add Erdos/Renyi (uniform) random graphs.