sphinx 4.1.x breaks tox docs test

[sydp]

Description of problem:

Running tox -e docs results in errors due to "broken" anchor links to github.

It seems this is related to a recent change in how sphinx handles github links (sphinx-doc/sphinx#9435).

Plaso version:

For example 20210606

Operating system Plaso is running on:

Ubuntu 20.04

Installation method:

Cloned repository then ran

cd plaso
tox -e docs

Debug output/tracebacks:

Partial output containing "broken" links:

(sources/user/Tagging-Rules: line    7) ok        https://github.com/log2timeline/plaso/blob/main/data/tag_linux.txt
(sources/user/Scribbles-about-events: line   76) broken    https://github.com/log2timeline/plaso/blob/48d83b11a3dcf8d191ccf441ef5aa29a2541e04c/plaso/containers/events.py#user-content-L10 - Anchor 'user-content-L10' not found
(sources/user/Tagging-Rules: line   58) ok        https://github.com/log2timeline/plaso/blob/main/data/tag_macos.txt
(sources/user/Tagging-Rules: line   76) ok        https://github.com/log2timeline/plaso/blob/main/data/tag_windows.txt
(sources/user/Scribbles-about-events: line   78) broken    https://github.com/log2timeline/plaso/blob/main/plaso/containers/events.py#user-content-L123 - Anchor 'user-content-L123' not found
(sources/user/Scribbles-about-events: line   79) broken    https://github.com/log2timeline/plaso/blob/main/plaso/containers/events.py#user-content-L192 - Anchor 'user-content-L192' not found
(sources/user/Scribbles-about-events: line   77) broken    https://github.com/log2timeline/plaso/blob/main/plaso/containers/events.py#user-content-L95 - Anchor 'user-content-L95' not found
(sources/user/Tips-and-Tricks: line   14) ok        https://github.com/log2timeline/plaso/commit/c81ef3aea9817646ea2846376ce9e2a83c7d5fe5
(sources/Troubleshooting: line    8) ok        https://github.com/log2timeline/plaso/commits/main
(sources/Troubleshooting: line   13) ok        https://github.com/log2timeline/plaso/issues

[joachimmetz]

Also looks like chardet is no longer installed, made some changes in the PR to not treat it as a direct dependency. It can probably be removed as a dependency if no longer required by requests.