Add an option to enable "show touches"

Add -t/--show-touches option to show physical touches while scrcpy is
running.

See <https://github.com/Genymobile/scrcpy/issues/96>.

app/src/command.c

@@ -4,10 +4,9 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "common.h"
 #include "log.h"
 
-#define ARRAY_LEN(a) (sizeof(a) / sizeof(a[0]))
-
 static const char *adb_command;
 
 static inline const char *get_adb_command() {