Some people use text modules instead of the `separator` key in the bar
section to better configure the separator (colors, fonts).
Since we disallowed the same module being used multiple times in #1534,
this will now print an error message.
This should help with this a bit.
Ref #1913
This removes the spacing tinkering when parsing format specs.
The following example uses the old behavoir:
format-test = <label-foo> <label-bar>
format-breaks = <label-foo><label-bar>/<bar-test>
`format-test` would replace all occurences of ' ' with the
a space string with defined `spacing` as its width. `format-breaks` would
not validate as the tags where split with ' ' as delimiter.
All that nonsense has been removed and each tag is extracted as is.
The `spacing` parameter can still be used to apply N extra whitespaces
between the tags, but it is now 0 by default.
