Detail of changes:
* Moved scrapy.core.manager.ExecutionManager class to scrapy.crawler.Crawler
* Added scrapy.project.crawler singleton to reference a singleton instance of
Crawler class (previously known as scrapymanager)
* Left an alias scrapy.core.manager.scrapymanager to scrapy.project.crawler for
backwards compatibility (to be removed in Scrapy 0.11)
- added telnet console documentation
- added documentation for debugging memory leaks with guppy
- sorted out shell alises
- set default port (TELNETCONSOLE_PORT) to 6023