message: single_context shouldn't permit appending of multiple values
diff: @@ -49,7 +49,7 @@ class single_context {
  /// @param _
  /// An open_document_type token
  ///
  - BSONCXX_INLINE key_context<single_context> operator<<(open_document_type) {
  + BSONCXX_INLINE key_context<> operator<<(open_document_type) {
  _core->open_document();
  return wrap_document();
  @@ -61,7 +61,7 @@ class single_context {
  /// @param _
  /// An open_array_type token
  ///
  - BSONCXX_INLINE array_context<single_context> operator<<(open_array_type) {
  + BSONCXX_INLINE array_context<> operator<<(open_array_type) {
  _core->open_array();
  return wrap_array();
  @@ -80,12 +80,12 @@ class single_context {
  }
  private:
  - BSONCXX_INLINE array_context<single_context> wrap_array() {
  - return array_context<single_context>(_core);
  + BSONCXX_INLINE array_context<> wrap_array() {
  + return array_context<>(_core);
  }
  - BSONCXX_INLINE key_context<single_context> wrap_document() {
  - return key_context<single_context>(_core);
  + BSONCXX_INLINE key_context<> wrap_document() {
  + return key_context<>(_core);
  }
  core* _core;
  