Merge pull request #8 from Flast/pr/doc/metafun

Fix return type in metafunction documentation

doc/reference/semantics.qbk

@@ -60,7 +60,7 @@
     ]
     [
         [`range_difference<X>::type`]
-        [`boost::iterator_category<range_iterator<X>::type>::type`]
+        [`boost::iterator_difference<range_iterator<X>::type>::type`]
         [compile time]
     ]
     [