adding a proper bash-completion generation

devscripts/bash_completion.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python2
+import youtube_dl
+
+BASH_COMPLETION_FILE = "youtube-dl.bash_completion"
+BASH_COMPLETION_TEMPLATE = "devscripts/bash_completion.template"
+
+def build_completion(opt_parser):
+    opts_flag = []
+    for group in opt_parser.option_groups:
+        for option in group.option_list:
+            #for every long flag
+            opts_flag.append(option.get_opt_string())
+    with open(BASH_COMPLETION_TEMPLATE) as f:
+        template = f.read()
+    with open(BASH_COMPLETION_FILE, "w") as f:
+        #just using the special char
+        print opts_flag
+        filled_template = template.replace("{{flags}}", " ".join(opts_flag))
+        f.write(filled_template)
+
+parser = youtube_dl.parseOpts()[0]
+build_completion(parser)