Using lucasdemarchi/codespell to fix typos

Generalize the file pipeline log messages

Fix some small typos and errors in docs

Added a mimetype parameter to `MailSender.send`

fixes dynamic itemclass example usage of type()

DupeFilter: add settings for verbose logging and filtered requests stats

CrawlSpider: support process_links as generator

Install twisted trunk because released twisted doesn't install properly,
see https://twistedmatrix.com/trac/ticket/6539.

Also, test-requirements are removed for 3.3 because mitmproxy doesn't
install in Python 3.3, and mock is in Python 3.3 standard library.

Note that trial scrapy is not doing what is expected because twisted doesn't
have trial runner for 3.3 yet, so this command will most likely call "trial"
outside tox virtualenv and will use incorrect interpreter.

DOC Use pipelines module name instead of pipieline following default project files.

fix a reference to unexistent engine.slots.

downloaderMW doc typo (spiderMW doc copy remnant)

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

[WIP] Handle cases when inspect.stack() fails

[MRG] testing PIL dependency is removed because there is a new mitmproxy version

Fix wrong checks on subclassing of deprecated classes