Add option --config-location

Add option --config-location

A configfile can now be passed to youtube_dl.

undo changes

Raise parser error if file not found, change to user_conf

change metavar hand helptext for --configfile

Fix help for --configfile

Update help for --configfile

Numbering placeholder in configfile error msg

minor fix

Change option --configfile top --config-file

Fix -config-file error