pluggable sub-commands for scrapy comand-line
added documentation (experimental feature)
Some changes to scrapy deploy command:

- use branch names when constructing HG/GIT versions
- added -d flag for debugging (keeps build directory)
- improved command output (redirected setup.py stderr)
added SEP-019 (per-spider settings) - first draft
sep-019: minor tide up
sep-019: fix typos
sep-019: other minor fixes
sep-019: remove TODO section (settled down with class method)
Merge pull request #260 from llonchj/entry_point

Commands module
updated AUTHORS
added #260 to release notes
add new sep-20 and update sep-19 with table at the top
Merge pull request #264 from stav/sep

add new sep-20 and update sep-19 with table at the top