Add separateWith, a method to set the separator

[SimonBarrettACT]

Thanks for the really useful package.

I found that I preferred to have no separator between the text and the badges, so hence this pull request.

The added section to read me explains it's use.

Separator

The default separator between the column text and the badges is '—'.
If you would like to use a different separator, use separateWith()
method to set the character to be used as a separator.

[awcodes]

Thanks. :)