May be used for quick check if not running an obsolete UG during
runtime.

(related to previous commmit)

Originally mute for both sender and receiver were dispatched by the
sender, which doesn't need to be present, however.

+ added SPOUT to Syphon for hide_window use case

Adding of displayed and corrupted frames was accidentaly removed by a779d96c.

This function may not be used at all but just to make sure.

- chech return value of getnatpmprequesttimeout()
- break the loop after 5 seconds (to avoid infinite loop)

It isn't double-released, anyway, but just for sure.

Smpte bars doesn't have the eight colum as EBU has.

Moreover the pattern is not complete - the bottom third contains
different data - mention this in help + todo.

GCC 11 gives incorrect warning for unintialized strerror_buf on
strerror_buf.size(), which is, however, compile-time constant. As a
workaround a separate size constant is used.

When uncompressed it requires less bandwidth and it is more suitable for
compression and/or further processing.

+ fail if audio BPS or sample rate is invalid rather than displaying
  only a warning
+ removed unused FRAME_TIMEOUT

Incorrect BPP (3) was used for RGBA

- use $(CXX) instead of hard-codec g++ in Makefile.convert
- conversion -> list-conversions + brief usage

fix type o found to find

+ small improvements (use of MAX_PATH_SIZE)

SDL, GL and NDI required mainloop only on macOS.

The export structure was not zero-initialized as expected when checked
for NULL.