init mmap graph
initial version of mgraph
Use unique_ptr to fix some memory leaks
first merge graph io
graph api
retab
add sync function for explicit save
merge mgraph, remove sample data

mgraph: add pointer types for {Edge,Vertex}Iterator
mgraph: add edge counts for VertexIterator
mgraph: added Clone interface
pagerank: use double instead of float
pagerank: added saedb as library dependency
merge pull request mgraph
fix engine counter bug & add memory graph target
merge map_reduce_vertices && retab
Merge from upstream/master