message: remove unneeded `fn main` from doctests
diff: @@ -107,15 +107,12 @@ impl<N, E, Ty, Ix> Csr<N, E, Ty, Ix>
  /// use petgraph::csr::Csr;
  /// use petgraph::prelude::*;
  ///
  - /// # fn main() {
  - ///
  /// let graph = Csr::<u8,()>::with_nodes(5);
  /// assert_eq!(graph.node_count(),5);
  /// assert_eq!(graph.edge_count(),0);
  ///
  /// assert_eq!(graph[0],0);
  /// assert_eq!(graph[4],0);
  - /// # }
  /// ```
  pub fn with_nodes(n: usize) -> Self
  where N: Default,
  @@ -152,15 +149,12 @@ impl<N, E, Ix> Csr<N, E, Directed, Ix>
  /// use petgraph::csr::Csr;
  /// use petgraph::prelude::*;
  ///
  - /// # fn main() {
  - ///
  /// let graph = Csr::<(),()>::from_sorted_edges(&[
  /// (0, 1), (0, 2),
  /// (1, 0), (1, 2), (1, 3),
  /// (2, 0),
  /// (3, 1),
  /// ]);
  - /// # }
  /// ```
  pub fn from_sorted_edges<Edge>(edges: &[Edge]) -> Result<Self, EdgesNotSorted>
  where Edge: Clone + IntoWeightedEdge<E, NodeId=NodeIndex<Ix>>,
  