Merge pull request #12 from levinkov/master

implementing algorithms for finding cut-vertices and cut-edges, with unit tests
Merge pull request #13 from levinkov/master

implementing MST and adding doxygen comments to cut vertices and bridges algorithms
updating README
updating README
updating README
updating README
updating README
updating README
updating README
updating README
updating doxygen
removing legacy code
fixing link in README
adding generic BFS and DFS with callbacks
updating README
updating README
removing size type template parameter from GridGraph, for consistency
Fixes: making edge lookup threadsafe and adding std::initialization_list
Merge pull request #14 from kalofoli/gridgraph-proposal

making edge lookup threadsafe and adding std::initialization_list