Improve some metavar names

youtube-dl

@@ -2000,22 +2000,22 @@ if __name__ == '__main__':
 		parser.add_option('-i', '--ignore-errors',
 				action='store_true', dest='ignoreerrors', help='continue on download errors', default=False)
 		parser.add_option('-r', '--rate-limit',
-				dest='ratelimit', metavar='L', help='download rate limit (e.g. 50k or 44.6m)')
+				dest='ratelimit', metavar='LIMIT', help='download rate limit (e.g. 50k or 44.6m)')
 		parser.add_option('-R', '--retries',
-				dest='retries', metavar='T', help='number of retries (default is 10)', default=10)
+				dest='retries', metavar='RETRIES', help='number of retries (default is 10)', default=10)
 
 		authentication = optparse.OptionGroup(parser, 'Authentication Options')
 		authentication.add_option('-u', '--username',
-				dest='username', metavar='UN', help='account username')
+				dest='username', metavar='USERNAME', help='account username')
 		authentication.add_option('-p', '--password',
-				dest='password', metavar='PW', help='account password')
+				dest='password', metavar='PASSWORD', help='account password')
 		authentication.add_option('-n', '--netrc',
 				action='store_true', dest='usenetrc', help='use .netrc authentication data', default=False)
 		parser.add_option_group(authentication)
 
 		video_format = optparse.OptionGroup(parser, 'Video Format Options')
 		video_format.add_option('-f', '--format',
-				action='store', dest='format', metavar='FMT', help='video format code')
+				action='store', dest='format', metavar='FORMAT', help='video format code')
 		video_format.add_option('-b', '--best-quality',
 				action='store_const', dest='format', help='download the best quality video possible', const='0')
 		video_format.add_option('-m', '--mobile-version',
@@ -2049,9 +2049,9 @@ if __name__ == '__main__':
 		filesystem.add_option('-l', '--literal',
 				action='store_true', dest='useliteral', help='use literal title in file name', default=False)
 		filesystem.add_option('-o', '--output',
-				dest='outtmpl', metavar='TPL', help='output filename template')
+				dest='outtmpl', metavar='TEMPLATE', help='output filename template')
 		filesystem.add_option('-a', '--batch-file',
-				dest='batchfile', metavar='F', help='file containing URLs to download (\'-\' for stdin)')
+				dest='batchfile', metavar='FILE', help='file containing URLs to download (\'-\' for stdin)')
 		filesystem.add_option('-w', '--no-overwrites',
 				action='store_true', dest='nooverwrites', help='do not overwrite files', default=False)
 		filesystem.add_option('-c', '--continue',