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/header/common/origin.rs

@@ -71,7 +71,7 @@ impl FromStr for Origin {
             Some(idx) => idx,
             None => return Err(::Error::Header)
         };
-        // idx + 3 because thats how long "://" is
+        // idx + 3 because that's how long "://" is
         let (scheme, etc) = (&s[..idx], &s[idx + 3..]);
         let host = try!(Host::from_str(etc));