Follow redirects

I have implemented following of redirects.

Currently only 301 is supported. I'm still working on this, but wanted to post it early so I can include any comments you have. :)

Some servers send data after the 301 header. To support this I used an own callback for the headers, to detect if a new request comes in. Maybe this can also help with the 100-continue responses.

Tell me what you think. :)