Make relativeTo and nonStrictRelative not wrap result in Maybe

The functions were always returning Just. Also, according to the RFC the
algorithm is not guaranteed to return an absolute URL.

Fixes #50.

Network/URI.hs

@@ -989,7 +989,7 @@ unEscapeString (c:s) = c : unEscapeString s
 --  Algorithm from RFC3986 [3], section 5.2.2
 --
 
-nonStrictRelativeTo :: URI -> URI -> Maybe URI
+nonStrictRelativeTo :: URI -> URI -> URI
 nonStrictRelativeTo ref base = relativeTo ref' base
     where
         ref' = if uriScheme ref == uriScheme base
@@ -999,9 +999,11 @@ nonStrictRelativeTo ref base = relativeTo ref' base
 isDefined :: ( MonadPlus m, Eq (m a) ) => m a -> Bool
 isDefined a = a /= mzero
 
--- |Compute an absolute 'URI' for a supplied URI
---  relative to a given base.
-relativeTo :: URI -> URI -> Maybe URI
+-- | Returns a new 'URI' which represents the value of the first 'URI'
+-- interpreted as relative to the second 'URI'.
+--
+-- Algorithm from RFC3986 [3], section 5.2
+relativeTo :: URI -> URI -> URI
 relativeTo ref base
     | isDefined ( uriScheme ref ) =
         just_segments ref
@@ -1034,7 +1036,7 @@ relativeTo ref base
             }
     where
         just_segments u =
-            Just $ u { uriPath = removeDotSegments (uriPath u) }
+            u { uriPath = removeDotSegments (uriPath u) }
         mergePaths b r
             | isDefined (uriAuthority b) && null pb = '/':pr
             | otherwise                             = dropLast pb ++ pr