ANYSIZE_ARRAY is defined to 1 in Windows winnt.h

Exitting is done with ptread_cancel() since EWS' serverStop() doesn't look
to stop the thread (it supposes that close() of the socket causes
interrupting accept() of the same socket, which isn't true in U21.04
and it is a hack anyway).

Cannot reuse the same buffer for silence, because in audio_play_alsa_write_frame()
it gets converted from signed to unsigned. If the frame is reused it
causes alternation between 0 and -127, causing a loud square wave to be
played.

Closes #183

It looks like the encoder performance is inferior for H.264 so setting
lower in order to manager real-time encoding.

Infinite GOP is useless for UltraGrid

Clang doesn't understand -Wno-old-style-declaration and this is easier.
The source isn't ours anyway.

Clang issues warning if 1.

Honored eg. by NVENC but can be used also by other codecs.

Use at least 8 slices (as it was set in the patch deleted in previous
commit) to allow reasonable parallelism.

Our custom changes are already in FFmpeg upstream.

Do not use always our usleep implementation on MSW - MSYS2/CLANG64 has
its own implementation.

Macro doesn't complain on inconsistent static/non-static declaration in
case that strcasecmp is already declared.

Pass frame rather than synchronizing over shared buffer.

+ removed unused synchronization variables in rtsp_state

SDP file may be open in a binary mode (tmpfile()) so strip <CR>.

+ fix reading of empty lines (output was not terminated)

The file may be opened in a text mode and then the byte count returned
by fread() is lesser.

Prevents init freeze.

Make audio/video state aggregate members of rtsp_state - there is no
need to have it allocated separately.

- sligtly rewritten init_rtsp() - make URI handling more clean and clear
- audio_rtsp_state/video_rtsp_state::control fixes (free + use always
heap string)

1. missing unlock
2. CV timeout and exit waiting when there is one - not to freeze when
there are no frames receive
3. do not trigger the boss CV when there is no data (for 2. to work)