g:auto_comma_or_semicolon needs "cosco" prefix for consistency

[atsepkov]

Thanks for the plugin, just started playing with it. I'm using the auto option, but I noticed that unlike g:cosco_ignore_comment_lines, and global options in most other plugins, it does not prefix the option with cosco, making it more likely to conflict with user's other variables and harder to find in vim file. Is that something that makes sense to add?

[lfilho]

Hey @atsepkov sure, sounds like a good suggestion. Would you be able to open a PR, please?