Move FileDownloader to its own module and create a new class for each download process

A suitable downloader can be found using the 'get_suitable_downloader' function.

Each subclass implements 'real_download', for downloading an info dict you call the 'download' method, which first checks if the video has already been downloaded

youtube_dl/downloader/__init__.py

@@ -0,0 +1,23 @@
+from .common import FileDownloader
+from .hls import HlsFD
+from .http import HttpFD
+from .mplayer import MplayerFD
+from .rtmp import RtmpFD
+
+from ..utils import (
+    determine_ext,
+)
+
+def get_suitable_downloader(info_dict):
+    """Get the downloader class that can handle the info dict."""
+    url = info_dict['url']
+
+    if url.startswith('rtmp'):
+        return RtmpFD
+    if determine_ext(url) == u'm3u8':
+        return HlsFD
+    if url.startswith('mms') or url.startswith('rtsp'):
+        return MplayerFD
+    else:
+        return HttpFD
+