doc: fix lints from rustdoc (#631)

Author: molpopgen

src/error.rs

@@ -62,7 +62,7 @@ pub fn get_tskit_error_message(code: i32) -> String {
     sys::get_tskit_error_message(code)
 }
 
-/// Given an instance of [``TskReturnValue``](crate::TskReturnValue),
+/// Given an instance of [``TskReturnValue``],
 /// obtain the tskit error message if there is indeed an error.
 pub fn extract_error_message(x: TskReturnValue) -> Option<String> {
     x.map_or_else(|e: TskitError| Some(format!("{}", e)), |_| None)

src/trees/treeseq.rs

@@ -292,7 +292,8 @@ impl TreeSequence {
     /// # Parameters
     ///
     /// * `lambda` specifies the relative weight of topology and branch length.
-    ///    See [`TreeInterface::kc_distance`] for more details.
+    ///   If `lambda` is 0, we only consider topology.
+    ///   If `lambda` is 1, we only consider branch lengths.
     pub fn kc_distance(&self, other: &TreeSequence, lambda: f64) -> Result<f64, TskitError> {
         self.inner.kc_distance(&other.inner, lambda)
     }