docs: pip upgrade recommonmark and CommonMark

Summary:
- recommonmark: 0.4.0 -> 0.5.0
- CommonMark: 0.5.4 -> 0.9.0
- Fixed links getting their .md file extension cut off
- Supressed 262 new warnings

Details:
Appended #anchors to markdown github links as a workaround to
recommonmark 0.5.0 cutting off the ".md" part from them.
Sphinx build would fail as follows

[documentation_crawler] ERROR: Please check link:
<404 https://github.com/zulip/zulipbot/blob/master/.github/CONTRIBUTING>
<404 https://github.com/zulip/zulip/blob/master/requirements/README>
<404 https://github.com/zulip/python-zulip-api/blob/master/zulip_bots/README>

sphinx build would also log a "WARNING: None:any reference target not found"
for every link ending in .html
So a good temporary solution is to suppress all warnings with the method suggested here:
https://stackoverflow.com/questions/37359407/suppress-warnings-for-unfound-references-with-default-role-any-in-sphinx

A better solution would be to edit all links ending .html and use .md instead;
which would also solve PR #11719.

Fixes #11395.

docs/conf.py

@@ -308,8 +308,18 @@ source_parsers = {
 # You can specify multiple suffix as a list of string:
 source_suffix = ['.rst', '.md']
 
+# Temporary workaround to supress warnings after upgrading to recommonmark==0.5.0
+# Otherwise, sphinx build complains about all the links ending in .html
+# See PR # for more details
+def on_missing_reference(app, env, node, contnode):
+    if node['reftype'] == 'any':
+        return contnode
+    else:
+        return None
+
 def setup(app: Any) -> None:
 
+    app.connect('missing-reference', on_missing_reference)
     app.add_config_value('recommonmark_config', {
         'enable_eval_rst': True,
         # Turn off recommonmark features we aren't using.

docs/contributing/zulipbot-usage.md

@@ -96,5 +96,5 @@ label "travis updates"`, and **@zulipbot** will let you know the build status
 If you wish to help develop and contribute to **@zulipbot**, check out the
 [zulip/zulipbot](https://github.com/zulip/zulipbot) repository on GitHub and read
 the project's [contributing
-guidelines](https://github.com/zulip/zulipbot/blob/master/.github/CONTRIBUTING.md) for
+guidelines](https://github.com/zulip/zulipbot/blob/master/.github/CONTRIBUTING.md#contributing) for
 more information.

docs/subsystems/custom-apps.md

@@ -307,7 +307,7 @@ We want to make it easier to deploy **Zulip Readers** on
 Zulip hardware.  The following document talks about how we want to enable this
 from a code structuring standpoint:
 
-[Writing contrib bots](https://github.com/zulip/python-zulip-api/blob/master/zulip_bots/README.md)
+[Writing contrib bots](https://github.com/zulip/python-zulip-api/blob/master/zulip_bots/README.md#zulip-bots)
 
 This document, on the other hand, is more about designing the Zulip backend
 system to support eventual deployment of reader apps on the Zulip server.

docs/subsystems/dependencies.md

@@ -231,7 +231,7 @@ super fast internet. You can use tmux or screen to make sure that the
 from the SSH session.
 
 [mypy-docs]: ../testing/mypy.html
-[requirements-readme]: https://github.com/zulip/zulip/blob/master/requirements/README.md
+[requirements-readme]: https://github.com/zulip/zulip/blob/master/requirements/README.md#requirements
 [stack-overflow]: https://askubuntu.com/questions/8653/how-to-keep-processes-running-after-ending-ssh-session
 [caching]: https://help.github.com/en/articles/caching-your-github-password-in-git
 

requirements/dev.txt

@@ -38,7 +38,7 @@ cffi==1.12.3              # via argon2-cffi, cryptography
 cfn-lint==0.22.3          # via moto
 chardet==3.0.4            # via requests
 click==7.0                # via gitlint, pip-tools
-commonmark==0.5.4
+commonmark==0.9.0
 constantly==15.1.0        # via twisted
 coverage==4.5.3
 cryptography==2.6.1       # via apns2, moto, pyopenssl, requests, service-identity, sshpubkeys
@@ -145,7 +145,7 @@ pytz==2019.1
 pyyaml==5.1.1             # via cfn-lint, moto, yamole
 qrcode==6.1               # via django-two-factor-auth
 queuelib==1.5.0           # via scrapy
-recommonmark==0.4.0
+recommonmark==0.5.0
 redis==3.2.1
 regex==2019.6.8
 requests-oauthlib==1.0.0  # via python-twitter, social-auth-core

requirements/docs.in

@@ -12,9 +12,9 @@ sphinx==1.8.4
 sphinx-rtd-theme==0.4.3
 
 # Needed to build markdown docs
-recommonmark==0.4.0
+recommonmark==0.5.0
 
 # Upgrading to the latest version of CommonMark breaks the
 # compatibility with recommonmark.  See
 # https://github.com/rtfd/recommonmark/issues/24
-CommonMark==0.5.4
+CommonMark==0.9.0

requirements/docs.txt

@@ -11,7 +11,7 @@ alabaster==0.7.12         # via sphinx
 babel==2.5.3              # via sphinx
 certifi==2019.6.16        # via requests
 chardet==3.0.4            # via requests
-commonmark==0.5.4
+commonmark==0.9.0
 docutils==0.14            # via recommonmark, sphinx
 idna==2.8                 # via requests
 imagesize==1.1.0          # via sphinx
@@ -21,7 +21,7 @@ packaging==19.0           # via sphinx
 pygments==2.4.2           # via sphinx
 pyparsing==2.4.0          # via packaging
 pytz==2019.1              # via babel
-recommonmark==0.4.0
+recommonmark==0.5.0
 requests==2.22.0          # via sphinx
 six==1.12.0               # via packaging, sphinx
 snowballstemmer==1.2.1    # via sphinx