Added support for redirect

[pinscript]

As requested in #84 (I also wanted it for the P-R-G pattern). I think this is the most flexible solution.

We could offer a Redirect(location string) which defaults to 302 and a RedirectCode(location string, code int). What do you think? I think people should be aware of what status code they are returning so the implemented solution is enough for me.

[manucorporat]

Sorry, I was in holidays.

I like it, but I would like to avoid the possibility to use:

c.Redirect("http://something", 200)

should we panic with non-3xx codes?

[pinscript]

Sure. According to RFC2616 (http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html), the following status codes can send a Location header: 201, 300, 301, 302, 303, 305, 307, 406.

Should we allow only theese status codes?

I think a panic would be best.

[manucorporat]

I guess so, since it's a high level API (called Redirect) we should not allow codes not specified by the standard.

[pinscript]

Added range checks for status code. I probably misinterpreted RFC2616, no major browser seem to follow locations for 201 and 406 codes.

After giving it some thought, I think we should go with the Redirect(code, location) signature. This is in line with the other render-methods (JSON, XML, etc).

[manucorporat]

Good job! Merged in develop: ceec1b6

Thank you so much ;)