readme: support experiment resource urls

A normal .pagespeed. url looks like:

    256x192vPuzzle.jpg.pagespeed.ic.alA0AdlR-2.jpg

If someone turns on RunExperiment, however, we generate urls like:

    256x192vPuzzle.jpg.pagespeed.a.ic.alA0AdlR-2.jpg
    256x192vPuzzle.jpg.pagespeed.b.ic.alA0AdlR-2.jpg

The new section is always a single letter between a and z.  We need to catch
these and pass them through to PageSpeed.
Merge pull request #162 from pagespeed/jefftk-experiment-resource-regexp

readme: support experiment resource urls
Solve "unknown type name ‘off64_t’", issue #166
Merge pull request #167 from jperelli/patch-1

Solve "unknown type name ‘off64_t’", issue #166
rewrite_driver_factory: move instantiation up front

We need to have the NgxRewriteDriverFactory available at configuration parse
time to set options on it. This change moves instantiation of the factory in
front of configuration parsing.  Afterwards, a check is done to see if we where
enabled anywhere.  If we where not enabled / do not have any active server
contexts, the NgxRewriteDriverFactory is deleted. It's not very elegant, but we
can't think of anything better currently.

Squash merge of Otto's #165.
message-handler: Add NgxMessageHandler

This adds an NgxMessageHandler, that uses ngx_log_error to output messages. It
is heavily based on apache_message_handler from mod_pagespeed.

It falls back to an internal GoogleMessageHandler if the required initialisation
has not been performed yet.

It can also install a crash handler, that will try to log a backtrace upon
receiving certain signals. In preparation of us porting /ngx_pagespeed_messages,
it also keeps the last few messages in a SharedCircularBuffer

(Squash-merge of Otto's #163)
Merge branch 'master' of https://github.com/pagespeed/ngx_pagespeed into oschaaf-statistics

Conflicts:
	src/ngx_pagespeed.cc
	src/ngx_rewrite_driver_factory.cc
	src/ngx_rewrite_driver_factory.h