Co-authored-by: NMikhail Korobov <kmike84@gmail.com>

* [docs] async/deferred signal handlers

* [docs] update deferred signals example

* [docs] add subsections for built-in signals

* docs(signals): update signal handler example

* docs(signals): update signal handler example

* modified debugging memory leaks with guppy in leaks.rst

* modified leaks.rst(issue #4285)

* removed guppy from telnet.py

* Fix undefined name error

* removed hpy key from telnet_vars in telnet.py

* updated shell.rst

* Update docs/topics/shell.rst
Co-Authored-By: NAdrián Chaves <adrian@chaves.io>
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

Docs: replace deprecated FEED_FORMAT and FEED_URI settings

Serialize requests with callback references as spider attribute

Fix pycodestyle E731 ("do not assign a lambda expression, use a def")

Get server IP address for HTTP/1.1 Responses

This code is not needed anymore because we're getting the
already mangled name when matching func with spider attributes.

Fix the hoverxref configuration

You could define a spider attribute that references a callback method
but if this method has a different name than your spider attribute,
the request serializer is not able to find it on the spider class.

With this commit we're fixing this behavior as we're searching for
callback references in the spider object itself instead of looking
for attributes with the same function's name, that could be different.

update redirect links to python3

[Docs] mention curl2scrapy in Request.from_curl

Remove twisted.internet.defer.returnValue occurrences

Pin version for Sphinx and extensions, configure hoverxref

Co-Authored-By: NAdrián Chaves <adrian@chaves.io>

Co-authored-by: Nsantosh <santosh@acalvio.com>

Handle StopIteration instead

Fix pycodestyle E502 ("the backslash is redundant between brackets")

Remove empty _RequestBodyProducer for POST requests