Hypergraph is data structure library to create a directed hypergraph in which a hyperedge can join any number of vertices.

The integration test in tests/test.rs seems to create an invalid dot file (which is normally just printed to the void and not actually used). The output is:

digraph {
    edge [penwidth=0.5, arrowhead=normal, arrowsize=0.5, fontsize=8.0];
    node [color=gray20, fontsize=8.0, fontcolor=white, style=filled, shape=circle];
    rankdir=LR;

    0 [label="Vertex {\l    name: \"d\",\l}\l"];
    1 [label="Vertex {\l    name: \"b\",\l}\l"];
    2 [label="Vertex {\l    name: \"c\",\l}\l"];


     [color="#0c8946", fontcolor="#0c8946", label="\"yup\"\l"];
     [color="#5309a3", fontcolor="#5309a3", label="\"foo_\"\l"];

    0 -> 2 [color="#5b7a07", fontcolor="#5b7a07", label="\"bar\"\l"];
}

It seems to be outputting two edges with connection zero nodes, so just the attributes are being printed? When I run this through dot it errors (because it expected "A -> B" befre the "[color=..."). Is this an error in the dot writing code which is producing vertices without members?

I was intrigued by this crate, but hadn't encountered hypergraphs before, so a link to a definition would be great. (Alternatively, or additionally, you might want to add a short definition of an ordered hypergraph to the README.)

Also, there's lots of useful background information in wikipedia which it wouldn't be appropriate to include in the README.

This PR is mostly about bringing index stability for vertices and hyperedges, as discussed in #14. This is a huge refactoring since all the public methods are now returning a Result with custom errors. This was also a good opportunity to tackle some bugs...

There are still some points to clarify / fix:

• [X] Update the readme - the generated documentation is not enough to understand what the project is about
• [X] Create a logo - nice to have
• [X] ~Adjust #16 - dot rendering - since the underlying structure has changed quiet significantly~ Won't do / dropping it from core

Would you be averse to me refactoring your graphviz code to use my new dot-writer library? Largely for my own selfish reasons (so I can put it through its paces and put it out in the world a bit), but arguably it could make your code more readable, strongly typed and terser?

Happy to do the pull request myself of course (I might have to anyway as it might be missing a function here or there that your dot output needs), and equally understand if you'd like to minimize dependancies / leave things as they are.