Shuffle files and functions around for more consistent naming and smaller files

src/diff/properties.jl

@@ -0,0 +1,9 @@
+# return a namedtuple of the lengths of the added/removed nodes/edges
+function length(diff::Diff)
+   return (
+      addedNodes = length(diff.addedNodes), 
+      removedNodes = length(diff.removedNodes), 
+      addedEdges = length(diff.addedEdges), 
+      removedEdges = length(diff.removedEdges)
+   )
+end