named_*(vertices)

[mtfishman]

Add support in functions like named_path_graph, named_grid, etc. for specifying custom vertex names with a function, dictionary, array, etc.

For example:

named_path_graph(["a", "b", "c"])
named_path_graph(v -> "v$v", 3)
named_grid(["a" "b"; "c" "d"])
named_grid(v -> "v$(v[1]),$(v[2])", (2, 2))