Add StringSet::cbegin() and StringSet::cend() (#459)

Signed-off-by: Juan Cruz Viotti <[email protected]>

Author: jviotti

src/evaluator/include/sourcemeta/blaze/evaluator_string_set.h

@@ -42,6 +42,8 @@ class SOURCEMETA_BLAZE_EVALUATOR_EXPORT StringSet {
 
   inline auto begin() const -> const_iterator { return this->data.begin(); }
   inline auto end() const -> const_iterator { return this->data.end(); }
+  inline auto cbegin() const -> const_iterator { return this->data.cbegin(); }
+  inline auto cend() const -> const_iterator { return this->data.cend(); }
 
 private:
 // Exporting symbols that depends on the standard C++ library is considered