dep: Add rapidyaml

dep/rapidyaml/include/c4/utf.hpp

@@ -0,0 +1,16 @@
+#ifndef C4_UTF_HPP_
+#define C4_UTF_HPP_
+
+#include "c4/language.hpp"
+#include "c4/substr_fwd.hpp"
+#include <stddef.h>
+#include <stdint.h>
+
+namespace c4 {
+
+substr decode_code_point(substr out, csubstr code_point);
+size_t decode_code_point(uint8_t *C4_RESTRICT buf, size_t buflen, const uint32_t code);
+
+} // namespace c4
+
+#endif // C4_UTF_HPP_