Adding Network.URI.escape

[Graham Klyne]

Ironically, even the standards groups have problems with these issues.
Cf. http://lists.w3.org/Archives/Public/uri/2010Jan/0001.html

Gwern Branwen wrote:
> Yes, it does demonstrate that the task is difficult and messy. As it
> is, the danger can easily be breezed through by someone who wants to
> get a job done - and that's just not the Haskell way!
> Can we leave the task to you? Even just your escapeHttpOrFileUri is an
> improvement.

I can't promise a deadline by which this will be achieved, but I am prepared to
add it to my TODO list...

#g