Update YamlIO documentation for the ScalarTraits class.

This patch adds the missing context parameter to the
input and output methods in ScalarTraits.

Differential Revision: http://reviews.llvm.org/D9173

llvm-svn: 236328

llvm/docs/YamlIO.rst

@@ -456,10 +456,10 @@ looks like:
 
     template <>
     struct ScalarTraits<MyCustomType> {
-      static void output(const T &value, llvm::raw_ostream &out) {
+      static void output(const T &value, void*, llvm::raw_ostream &out) {
         out << value;  // do custom formatting here
       }
-      static StringRef input(StringRef scalar, T &value) {
+      static StringRef input(StringRef scalar, void*, T &value) {
         // do custom parsing here.  Return the empty string on success,
         // or an error message on failure.
         return StringRef();