DOWNLOAD_DELAY docs clarification:

* delay is enforced per website, not per spider;
* document download_delay attribute (it was previously documented only in FAQ about 999 error codes);
* document how CONCURRENT_REQUESTS_PER_IP affects download delays.
Clarify return value from extract_links
Promote startup info on settings and middleware to INFO level
Merge pull request #520 from redapple/startupinfo

Promote startup info on settings and middleware to INFO level
warn on XPathItemLoader subclassing
test_command_deploy, test_contrib_linkextractors
RegexLinkExtractorTestCase
RobotsTxtMiddlewareTest
Changed TOR Info as previous was removed from www.mininova.org
fixed error on tor's name
Merge pull request #527 from ferdyrod/master

Torrent url in the "Scrapy at a glance" doc was removed
Fix MemoryUsage extension for OS X. Fix GH-529.
Merge pull request #530 from kmike/memusage-osx

Fix MemoryUsage extension for OS X
Fix logging of stats collected by MemoryDebugger extension.

Stats are printed on spider_closed event;
engine_stopped signal is called after spider_closed signal,
so stats for MemoryDebugger extension were not printed to user.
Merge pull request #531 from kmike/fix-memdebug

Fix logging of stats collected by MemoryDebugger extension.
Merge pull request #523 from dangra/warn-xpathitemloader-subclass

warn on XPathItemLoader subclassing
Merge pull request #517 from hoprocker/patch-1

Clarify return value from extract_links
Merge pull request #502 from scrapy/doc-fixes

DOWNLOAD_DELAY docs clarification
Added "six>=1.5.2" to requirements
Removed deploy test (as deploy command is deprecated and moved to scrapyd)