indegree and outdegree
found a bug in shortest path

  only works along directed edges, even in graphs
fixed shortest-path bug
three centrality metrics

   :betweenness :closeness :farness
Merge branch 'master' into gh-pages
update
graph conversion to adjacency matrix
bidirectional adjacency matrix conversion
kratz centrality
pass functions to label nodes/edges in dot export

 e.g., (to-dot *graph* :node-label (curry #'katz-centrality *graph*))
Merge branch 'master' into gh-pages
update