Add documentation.

source/lib.rs

@@ -114,6 +114,7 @@ impl Generator {
 
   /// Returns all configurable options as a query parameter string.
   pub fn query_parameters(&self) -> String {
+    /// Shorthand for [`urlencoding::encode`].
     fn encode<D: std::fmt::Display>(data: D) -> String {
       urlencoding::encode(&data.to_string()).into_owned()
     }