[libmicrohttpd] new MHD demo

[Christian Grothoff]

Hi everyone,

I just wanted to let you know that I just finished writing a 'just for fun' 
demo for
MHD, showing how to do GET and POST with form processing, file upload and error
handling.  I tried to comment the code a lot as I hope it will be educational 
for some.

You can find it at
      https://gnunet.org/svn/libmicrohttpd/src/examples/demo.c
The code requires libmagic for mime-type detection (configure now checks for it;
however, libmagic is ONLY a dependency for the demo, not for anything else).

I mostly used the demo to benchmark MHD a bit, as someone online claimed 'bad' 
POST
processing performance.  As a result, SVN HEAD now also includes some minor 
performance
improvements; however, I suspect for most users they make little to no 
difference.
(If we're not IO-bound, I see speeds exceeding 1.5 GB/s for POST and 2 GB/s for 
GET
on my desktop, which to me seems fast enough; in any case, if someone has a 
benchmark
that still shows a real issue, please do let me know.)


Happy hacking!

Christian