Changed the wording of the documentation for the insert method for Vec to be less confusing. Since 0 is the smallest number possible for usize, it doesn't make sense to mention it if it's already included, and it should be more clear that the length of the vector is a valid index with the new wording.

Author: djallen89

src/libcollections/vec.rs

@@ -525,8 +525,7 @@ impl<T> Vec<T> {
     ///
     /// # Panics
     ///
-    /// Panics if `index` is not between `0` and the vector's length (both
-    /// bounds inclusive).
+    /// Panics if `index` is greater than the vector's length.
     ///
     /// # Examples
     ///