Add crop feature

Add an option to crop the screen on the server. This allows to mirror
only part of the device screen.

app/src/scrcpy.c

@@ -126,7 +126,7 @@ static void wait_show_touches(process_t process) {
 
 SDL_bool scrcpy(const struct scrcpy_options *options) {
     if (!server_start(&server, options->serial, options->port,
-                      options->max_size, options->bit_rate)) {
+                      options->max_size, options->bit_rate, options->crop)) {
         return SDL_FALSE;
     }