Merge pull request #250 from ClickHouse/Enmk-deprecated-StringView

Deprecated StringView

Author: Enmk

clickhouse/base/string_view.h

@@ -11,7 +11,9 @@ template <
     typename TChar,
     typename TTraits = std::char_traits<TChar>
 >
-class StringViewImpl {
+class
+[[deprecated("Obsolete due to C++17's std::string_view. Will be removed in next major release (3.0) ")]]
+StringViewImpl {
 public:
     using size_type = size_t;
     using traits_type = TTraits;