Links in doc don't work on docs.rs

[Arne Keller]

Idk if this is fixable on your side, but this is what it looks like on https://docs.rs/daggy: (working links are *marked*)

The most prominent type is *Dag* - a wrapper around *petgraph* (http://bluss.github.io/petulant-avenger-graphlibrary/doc/petgraph/index.html)'s [Graph] (http://bluss.github.io/petulant-avenger-graphlibrary/doc/petgraph/graph/struct.Graph.html) data structure, exposing a refined API targeted towards directed acyclic graph related functionality.