adding some xpath tips to selectors docs
Merge pull request #815 from nramirezuy/retry_timeout-583

renamed UserTimeoutError and ServerTimeouterror #583
improved explanations, clarified blog post as source, added link for XPath string functions in the spec
removes weird indentation in the shell results
Merge pull request #814 from eliasdorneles/adding-some-xpath-tips

Adding some xpath tips to selectors docs
Add from_crawler class method to base Spider
Delete Spider properties crawler and settings, since they are now directly set
Deprecate and fixup set_crawler method in Spider class
Extract common functionality in Spider crawler methods
Connect spider_closed signal after a crawler is bounded to a Spider instance
Add from_crawler and deprecated set_crawler Spider tests
Change import order in test_spider
Overwrite from_crawler method as well as set_crawler on CrawlSpider
Add deprecate helper for the change of functions signatures
New init method implementation in Crawler
Extract common functionality in Crawler init implementations
Deprecate old crawl method in Crawler
New crawl method implementation in Crawler
Add [spiders] section to scrapy.cfg template, with manager and modules settings
Deprecate SPIDER_MANAGER_CLASS and SPIDER_MODULES settings