Add a formatter for folly::StringPiece

include/fmt/folly.h

@@ -0,0 +1,22 @@
+// Formatting library for C++ - folly::StringPiece formatter
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#ifndef FMT_FOLLY_H_
+#define FMT_FOLLY_H_
+
+#include <folly/Range.h>
+#include "core.h"
+
+FMT_BEGIN_NAMESPACE
+template <typename Ctx>
+inline internal::typed_value<Ctx, internal::string_type>
+    make_value(folly::StringPiece s) {
+  return string_view(s.data(), s.size());
+}
+FMT_END_NAMESPACE
+
+#endif  // FMT_FOLLY_H_