Handle resized video stream

Accept a parameter to limit the video size.

For instance, with "-m 960", the great side of the video will be scaled
down to 960 (if necessary), while the other side will be scaled down so
that the aspect ratio is preserved. Both dimensions must be a multiple
of 8, so black bands might be added, and the mouse positions must be
computed accordingly.

app/src/scrcpy.h

@@ -3,6 +3,6 @@
 
 #include <SDL2/SDL_stdinc.h>
 
-SDL_bool scrcpy(const char *serial, Uint16 local_port);
+SDL_bool scrcpy(const char *serial, Uint16 local_port, Uint16 maximum_size);
 
 #endif