escape special chars in username: - . \ @

[revarcline]

Regarding #387 - for my intended use of wetty we are all using usernames with periods in them. This PR allows the following characters for usernames: -, ., \, and @ I presume there may be a security reason that these are not allowed, so if this PR is not accepted, would one with an --insecure-characters flag possibly work?

[paulierco]

I can confirm that this works as expected. Thanks for sharing this.

[butlerx]

Please fix the lining errors and once the test pass I can merge.
Please also add tests to the spec file for the username styles you require

[revarcline]

done, thanks for the feedback (fwiw i skipped the no-useless-escape rule on the regex line)