[techtalks] Add support for playlists

[taitelman]

$ youtube-dl  --verbose  http://techtalks.tv/conll_2016/
[debug] System config: [u'--prefer-free-formats']
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'--verbose', u'http://techtalks.tv/conll_2016/']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2019.01.02
[debug] Python version 2.7.5 (CPython) - Linux-3.10.0-862.14.4.el7.x86_64-x86_64-with-redhat-7.5-Maipo
[debug] exe versions: ffmpeg 3.4.5, ffprobe 3.4.5
[debug] Proxy map: {}
[generic] conll_2016: Requesting header
WARNING: Falling back on generic information extractor.
[generic] conll_2016: Downloading webpage
[generic] conll_2016: Extracting information
ERROR: Unsupported URL: http://techtalks.tv/conll_2016/
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/youtube_dl/extractor/generic.py", line 2337, in _real_extract
    doc = compat_etree_fromstring(webpage.encode('utf-8'))
  File "/usr/lib/python2.7/site-packages/youtube_dl/compat.py", line 2542, in compat_etree_fromstring
    doc = _XML(text, parser=etree.XMLParser(target=_TreeBuilder(element_factory=_element_factory)))
  File "/usr/lib/python2.7/site-packages/youtube_dl/compat.py", line 2531, in _XML
    parser.feed(text)
  File "/usr/lib64/python2.7/xml/etree/ElementTree.py", line 1642, in feed
    self._raiseerror(v)
  File "/usr/lib64/python2.7/xml/etree/ElementTree.py", line 1506, in _raiseerror
    raise err
ParseError: syntax error: line 4, column 0
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/youtube_dl/YoutubeDL.py", line 793, in extract_info
    ie_result = ie.extract(url)
  File "/usr/lib/python2.7/site-packages/youtube_dl/extractor/common.py", line 508, in extract
    ie_result = self._real_extract(url)
  File "/usr/lib/python2.7/site-packages/youtube_dl/extractor/generic.py", line 3320, in _real_extract
    raise UnsupportedError(url)
UnsupportedError: Unsupported URL: http://techtalks.tv/conll_2016/

• I've verified and I assure that I'm running youtube-dl 2019.01.02
• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

What is the purpose of your issue?

• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
• Question
• Other