CrawSpider: support process_links as generator

Adding tests for CrawlSpider's process_links
Handle cases when inspect.stack() fails
testing PIL dependency is removed because there is a new mitmproxy version
Fix wrong checks on subclassing of deprecated classes. closes #581
Merge pull request #584 from dangra/581-deprecated-subclass-fix

Fix wrong checks on subclassing of deprecated classes
Merge pull request #585 from kmike/mitmproxy-reqs-cleanup

[MRG] testing PIL dependency is removed because there is a new mitmproxy version
test inspect.stack failure
Merge pull request #582 from kmike/inspect-workaround

[WIP] Handle cases when inspect.stack() fails
localhost666 can resolve under certain circumstances

localhost666 is resolvable if the host running the tests contains a
"search mydomain.com" in /etc/resolv.conf and a wildcard dns entry
exists for *.mydomain.com
Add 0.22.1 release notes
Correct typos
downloaderMW doc typo (spiderMW doc copy remnant)
Merge pull request #590 from Digenis/master

downloaderMW doc typo (spiderMW doc copy remnant)
add SEP-021 (Add-ons) - work in progress
fix a reference to unexistent engine.slots. closes #593
Merge pull request #594 from dangra/593-engineslots

fix a reference to unexistent engine.slots.
Add 0.22.2 release notes
DOC Use pipelines module name instead of pipieline following default project files.
Merge pull request #596 from darkrho/doc-pipeline

DOC Use pipelines module name instead of pipieline following default project files.
remove references to deprecated scrapy-developers list