AjaxCrawlableMiddleware
add an undocumented setting for lookup body size
Fail-fast path.

For me middleware now can process about 2-3k ajax crawlable pages/sec and 50k+ regular pages/sec (if they don’t contain «fragment» or «content» words).
extra test
AjaxCrawlableMiddleware in Broad Crawl docs
kill AjaxCrawlableMiddlewar.enabled_setting
add a remark about 1%
documentation code example correction corrections per pablohoffman
support showing subclassing deprecation warning only once
revert warning filter on deprecated class instantiation
only warn on direct subclasses of the deprecated class
split subclassing tests and default to warning only once per deprecated class
allow deprecation of a class with custom metaclass
allow overriding old and new class paths
allow deprecation of subclasses of already deprecated classes
another import name correction by pablo
Fix comment typo
Merge pull request #536 from manfre/patch-1

Fix comment typo
remove "for brevity's sake" line and correct "Torrent item"

Torrent item -> TorrentItem class
do not test multiple instantation warnings