Update Graphs.m2

This is the all new Graphs package.
Update GraphicalModels.m2

Modified trekSeparation to stop monkeying around *inside* a Digraph.  Fixed a type in the example of directedEdgesMatrix documentation.
Update Posets.m2

Lots of small changes.
Update Graphs.m2

Modified addEdges to not break NautyGraphs.
Update Graphs.m2

Adjust for the vertices symbol in SimplicialComplexes.
Update GraphicalModels.m2
Update Graphs.m2
Update Nauty.m2
Update NautyGraphs.m2
Update Posets.m2
Update SimplicialDecomposability.m2
Update Graphs.m2
Update GraphicalModels.m2
Update NautyGraphs.m2
Merge remote-tracking branch 'upstream/pull/120' into merging-120-take-2
Update Graphs.m2
Merge remote-tracking branch 'upstream/pull/120' into merging-120-take-2