Add --hls-use-mpegts option

When using the mpegts container hls vidoes can be played while being downloaded (useful if you are recording a live stream).
VLC and mpv play them file, but QuickTime doesn't.

youtube_dl/options.py

@@ -415,6 +415,11 @@ def parseOpts(overrideArguments=None):
         '--hls-prefer-native',
         dest='hls_prefer_native', action='store_true',
         help='Use the native HLS downloader instead of ffmpeg (experimental)')
+    downloader.add_option(
+        '--hls-use-mpegts',
+        dest='hls_use_mpegts', action='store_true',
+        help='Use the mpegts container for HLS videos, allowing to play the '
+             'video while downloading (some players may not be able to play it')
     downloader.add_option(
         '--external-downloader',
         dest='external_downloader', metavar='COMMAND',