implementing client certificate support

[Sean Conner]

It was thus said that the Great Michael Lazar once stated:
> 
> Heck, drop client certificates from the gemini specification all together.
> Judging by the lack of client support so far, it's becoming clear that either:
> 
> 1. They're a pain to implement compared to the rest of the specification
> 2. There's not much interest in actually using them

  I personally would like to keep them, if only to protect sections of a
Gemini site from general consumption.  The "transient client certificate"
idea is certainly problematic and I wouldn't mind if that concept went away
though.

  -spc