Tabs and double quotes not parsed correctly in authorized_keys file

authorized_keys files allow tabs as separators, backslash-escaped double quotes in option values and require double quotes around option values.

These cases are not treated correctly by sshpubkeys.AuthorizedKeysFile. See attached example file for test cases.
ak.txt

Feel free to create a PR to fix that. I'm happy to review and merge if test cases are included in the PR.