added markdown metadata parsing

src/markdown.hpp

@@ -0,0 +1,20 @@
+#include <optional>
+#include <set>
+#include <string>
+
+struct Metadata {
+  std::string author;
+  std::string date;
+  std::string title;
+  std::set<std::string> tags;
+};
+
+// Reads the metadata of the markdown file
+// Metadata are in yaml format at the top of the file
+// They are separated from the rest of the file with `---` at the beginning and
+// at the end.
+std::optional<Metadata> get_metadata(const std::string &FILE_PATH);
+
+// Reads the markdown file and converts it to html.
+// Return everything in one string
+std::string get_html(const std::string &FILE_PATH);