moved files out of subdirectories, added required documentation

src/merchant.h

@@ -0,0 +1,14 @@
+#ifndef __MERCHANT_H__
+#define __MERCHANT_H__
+
+#include "enemy.h"
+
+class merchant final: public enemy_base {
+public:
+        merchant(RNG *rng, const feature enabled_features, const position &pos,
+                 const int gen_room_num);
+        const char *get_race_name() const override;
+        int dies(level *lvl) override;
+};
+
+#endif