simple nonce checking function

I have seen quite some implementations on top of this library that do not perform any nonce checking.
Are there any objections to implement this within the library?
This pull request consists of a very primitive attempt :)
With this, I am hoping to prevent some trivial replay attacks and am looking forward to any kind of feedback.
If this here gets positive feedback, I'm inclined to handle timestamp checks prior to the nonce (baiscally move it out of the nonceFunction errback in lines 211-226 and execute it beforeline 209).

Tests missing, but I'm happy to spend some additional cycles on it, if this whole nonce thing is generally acceptable to you.