Support [sic] for typographical/spelling errors

[rugk]

I have a small feature request for csquotes: It would be great if we could have a auxiliary command for [sic] see [1] for marking typographical errors in quotations.

It may be international, but may also be localized via babel, so IMHO it is useful to add.

We already have \textelp and \textins and IMHO they would fall in the same category and make this package very useful.

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I already submitted this via mail and received a reply, but I still think it is a useful addition or at least useful to discuss with the community.