Improve the include situation

Slightly clean up header inclusion with the help of clang's module system.
It's better for files to include the things you need directly.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/compton.h

@@ -34,6 +34,10 @@
 #include "x.h"
 #include "c2.h"
 #include "log.h" // XXX clean up
+#include "region.h"
+#include "compiler.h"
+#include "types.h"
+#include "utils.h"
 #include "render.h"
 
 // == Functions ==