added database

src/database.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <sqlite3.h>
+#include <pthread.h>
+
+extern sqlite3 *db;
+extern pthread_mutex_t db_mutex;
+
+void init_db();
+void migrate_db();
+char* json_escape(const char* str);