Update using.dox

typo
Merge pull request #147 from larryxiao/master

Update using.dox, a typo

Thanks!!
Initial content for betweeness and prestige measures
initial draft for betweeness
Merge branch 'master' of https://github.com/graphlab-code/graphlab into prestige
Minor changes. Mostly updating access to include a SSH key
Djikstra and betweeness now compile.  Plenty of work for tomorrow finishing debugging.
Updates to djikstra and betweeness algorithms
closeness and prestige fixes