Makefile more thorough + better organization

Makefile

@@ -4,7 +4,7 @@ SRCDIR = src
 BUILDDIR = build
 TARGET = main
 
-SOURCES = $(wildcard $(SRCDIR)/*.c)
+SOURCES = $(wildcard $(SRCDIR)/**/*.c $(SRCDIR)/*.c)
 OBJECTS = $(patsubst $(SRCDIR)/%.c, $(BUILDDIR)/%.o, $(SOURCES))
 
 ifeq ($(OS),Windows_NT)
@@ -23,7 +23,7 @@ $(EXECUTABLE): $(OBJECTS)
 	$(CC) $(CFLAGS) -o $@ $^
 
 $(BUILDDIR)/%.o: $(SRCDIR)/%.c
-	$(MKDIR) $(BUILDDIR)
+	@$(MKDIR) -p $(@D)
 	$(CC) $(CFLAGS) -c -o $@ $<
 
 clean:

src/engine.h

@@ -1,8 +1,8 @@
 #ifndef __ENGINE_HEADER
 #define __ENGINE_HEADER
 
-#include "board.h"
+#include "engine/board.h"
-#include "common.h"
+#include "engine/common.h"
-#include "fen.h"
+#include "engine/fen.h"
 
 #endif // !__ENGINE_HEADER