Resolved issue #546. Output format parsing from filename extension.
Added back `-t` option. If `--output-format` not defined parse from extension `--output`
Fix default value.
Add import os for crawl.
Added more verbose error message for unrecognized output format. PEP8.
make scrapy.version_info a tuple of integers
New tox env: docs
Ignore known broken links in docs linkcheck
Fix broken links in documentation
Merge pull request #687 from Curita/docs-linkcheck

Docs build and linkcheck in tox env
Merge pull request #681 from kmike/version_info

[MRG] make scrapy.version_info a tuple of integers
Merge pull request #659 from denysbutenko/master

[MRG] Resolved issue #546. Output format parsing from filename extension.
remove unused import
cleanup toplevel namespace
Add basic top-level shortcuts
use "import scrapy" in templates
DOC use top-level shortcuts in docs
suggest scrapy.Selector in deprecation warnings
TST fix tests that became broken after adding top-level imports and switching to py.test.

py.test replaces AssertionError exception with its own subclass in an import hook.
For some reason when top-level shortcuts were added "except AssertionError" in
contracts.__init__ meant "except py.test AssertionError" while scrapy.exceptions.ContractFail
was still a subclass of a builtin AssertionError, so Contracts reported errors
instead of failures and this made tests in test_contracts.py fail.

For now - just disable fancy py.test asserts.