Add support for soundcloud tags

[treaki]

it advised me to report this:

$ youtube-dl https://soundcloud.com/tags/folk
[soundcloud] tags/folk: Resolving id
[soundcloud] tags/folk: Downloading info JSON
ERROR: Unable to download JSON metadata: HTTP Error 404: Not Found (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
$ youtube-dl --verbose https://soundcloud.com/tags/folk
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['--verbose', 'https://soundcloud.com/tags/folk']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2015.01.16
[debug] Python version 2.7.8 - Linux-3.16-3-amd64-x86_64-with-debian-8.0
[debug] exe versions: avconv 2.4.3, avprobe 2.4.3, ffmpeg 2.4.3, ffprobe 2.4.3, rtmpdump 2.4
[debug] Proxy map: {}
[soundcloud] tags/folk: Resolving id
[soundcloud] tags/folk: Downloading info JSON
ERROR: Unable to download JSON metadata: HTTP Error 404: Not Found (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 293, in _request_webpage
    return self._downloader.urlopen(url_or_request)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1412, in urlopen
    return self._opener.open(req, timeout=self._socket_timeout)
  File "/usr/lib/python2.7/urllib2.py", line 410, in open
    response = meth(req, response)
  File "/usr/lib/python2.7/urllib2.py", line 523, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.7/urllib2.py", line 448, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.7/urllib2.py", line 382, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 531, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)

[RCcola1987]

Is this ever going to be working?