Getting `recur` to work required adding an Operation argument to a bunch
of places in a really hacky way. I don't like it at all, but I'm also
kind of out of mental energy to figure it out properly. The fibonacci
demo in the README _works_, at least, though I don't think it's actually
tail recursive.
The base graph implementation has been moved into its own package,
`graph`, and been made fully generic, ie the value on each vertex/edge
is a parameterized type. This will allow us to use the graph for both
syntax parsing (gg) and runtime evaluation (vm), with each use-case
being able to use slightly different Value types.
The vm does what it needs to do (evaluate the result of passing an input
to an operatio, where the input and the operation themselves may have
sub-inputs/operations to evaluate), with many caveats/misgivings.
