clogger 0.5.0 - body.to_path forwarding

This release allows middleware like Rack::Contrib::Sendfile to
work properly higher up the stack from Clogger.

Certain configurations of the Rainbows! and Zbatery web servers
are able to use the return value of body.to_path to serve static
files efficiently (via IO.copy_stream under 1.9 or
stream_file_data with EventMachine).

There are some small cleanups and documentation improvements
as well.

I've relicensed to LGPLv2.1+ (from LGPLv3-only) to allow
bundling with GPLv2-only applications (I'm currently the sole
copyright holder).

Signed-off-by: Eric Wong <normalperson@yhbt.net>