Added cloning and counting to graphs.
Added edge map to graph builder.
Implemented working version of spanning tree iterator.
Made test folder of graph package a package itself.
Fixed imports on graph test.
Added sample tree with three spanning trees to sample graphs.
Handle edge case of empty graph when finding spanning tree.
Improved graph builder to conform to self returning builder pattern.
Added some sample graphs and changed all sample graph construction to use builder call chain.
Improved unit tests for spanning tree iteration.