clogger v2.2.0 - Rack 2.x compatibility fix

This release fixes a Rack compatibility problem when
Rack::BodyProxy wraps the Clogger object and calls
"respond_to?" with two arguments.  This affects folks
who put Clogger at lower levels of the middleware stack
(below middlewares which use Rack::BodyProxy)

A huge thanks to Pat Allan for coming up with this fix.

Note, the recommended usage of clogger middleware is to have
it at the outermost layer of the Rack middleware stack where
it can give the most accurate $request_time measurement.

There's also a couple of tiny internal improvements
around the build and miniscule GC overhead reduction.

Pat Allan (1):
      Update respond_to? calls for second argument.

Eric Wong (3):
      clogger.c: comment to explain the lack of GC guard
      ext: reduce frozen string marking overhead
      build: remove build-time olddoc dependency