fix(lib): Fixed typos in multiple modules

BREAKING CHANGE: The `Preference` header had a typo in a variant and it's string representation,
  change `Preference::HandlingLeniant` to `Preference::HandlingLenient`.

src/client/request.rs

@@ -34,7 +34,7 @@ impl Request {
     #[inline]
     pub fn url(&self) -> &Url { &self.url }
 
-    /// Readthe Request Version.
+    /// Read the Request Version.
     #[inline]
     pub fn version(&self) -> &HttpVersion { &self.version }