tip of graph_dev

changed structure of graph.cpp
new arc function to add vertices on the fly
commented out other graph algorithms for future development
emptied test.cpp
made maxflow nondestructive for cap, added test
Make maxflow incremental

When running with same ini and end, will reuse existing flow.
Otherwise, will clear flow before computing.
Merge pull request #7 from danielf/graph_dev_maxflow

updated maxflow algorithm
revert back to [init] for graph

this is to fix the bug that we cannot create graph with
nodes but without arcs
make [init] clear the whole graph
Merge pull request #8 from danielf/graph_dev_init

revert back to [init] for graph

Before this, we could not have vertices with larger ids than the largest vertex with arcs.
change graph to use constructor instead of [init]
Update graph.cpp
Merge pull request #9 from danielf/graph_dev_constructor

change graph to use constructor instead of [init]
added typedef vector<double> vd
implememnted mincostflow(with debug output)

doesn't introduce new source and sink in solving
removed debug info
Merge pull request #10 from danielf/graph_dev_mincostflow

Graph dev mincostflow
bug fix, use [ent] instead of [dist] as mark

if there is 0 cost arc, it's possible that the shortest dist
is exactly inf
Merge pull request #11 from danielf/graph_dev_mincostflow

bug fix, use [ent] instead of [dist] as mark
rewrote artp and bridge and tested it
rewrote and tested scc
rewrote and tested twosat
removed 2sat from graph

it's so easy, so I removed it