Improve performance of Hatchet Graphs using igraph

[ilumsden]

While looking into C++ graph libraries for a personal project, I discovered the igraph library. It is a extremely versatile graph library that's written in C/C++ and has bindings to C, Python, R, etc.

Given that there have been performance concerns with respect to certain functionality in Hatchet's Graph class, I'm wondering if it would be possible to reimplement the Graph class using the Python version of igraph.

One thing to note, if we were to do this, the reimplementation would involve moving some functionality (e.g., traverse, dag_equal) out of the Node class and into the Graph class. This would technically be a backwards compatibility-breaking change to Hatchet's API.

I'm opening this issue for discussion of the idea.