Feature request: support some GraphViz features

[DavidBJaffe]

Hi -- this crate is really cool!!

I tested an example

digraph G {
node [width=0.13,height=0.13,fontsize=10,shape=point];
edge [fontsize=18,penwidth=1.3,arrowsize=1.3,fontname=Arial];
rankdir=LR;
labeljust=l;
margin=0;
15 -> 10 [minlen=2,color=red,label="0 (len=173,supp=807)"];
5 -> 15 [minlen=2,color=red,label="1 (len=430,supp=1567)"];
10 -> 7 [minlen=1,color=black,label="2 (len=26,supp=541)"];
7 -> 10 [minlen=1,color=black,label="3 (len=30,supp=951)"];
0 -> 7 [minlen=2,color=red,label="4 (len=618,supp=3220)"];
14 -> 13 [minlen=2,color=red,label="5 (len=632,supp=269)"];
11 -> 15 [minlen=1,color=black,label="6 (len=43,supp=40)"];
}

and got this output

as compared to what running dot yields

It would be awesome to get closer to the dot output.

Thank you very much!!