[MRG+1] PY3 fix downloader slots GC

[MRG+1] Fix bug on XMLItemExporter with non-string fields in items

[MRG+1] shell command's ability to open local files + tests

[MRG+1] Include tests for non-string items to Exporters

[MRG+1] micro-optimize response.text

[MRG+1] Fix PythonItemExporter and CSVExporter for non-string item types

[MRG+1] Clarify priority adjust settings docs

[MRG+1] Add Code of Conduct Version 1.3.0 from http://contributor-covenant.org/

[MRG+1] response.text

Fixes #1593

[MRG+1] Disable SpiderState extension if no JOBDIR set

Use long classes names for enabled middlewares in startup logs

[MRG+1] Enable robots.txt handling by default for new projects.

For backwards compatibility reasons the default value is not changed.

[MRG+1] Disable CloseSpider extension if no CLOSPIDER_* setting set

[MRG+1] deprecated unused and untested code in scrapy.utils.datatypes