Add dark mode to documentation

[iamdefinitelyahuman]

What was wrong?

1. The documentation had no dark mode.
2. The documentation had some minor formatting issues.

How was it fixed?

1. I added a dark mode toggle button.
2. While verifying the dark mode, I fixed any formatting issues that I noticed.

Dark Mode

• docs/_templates/versions.html expands on the the builtin template's version.html, which is the version selection in the bottom left. I abbreviated "Read the Docs" to "RTD" and added a slider that toggles day/night. Related sphinx documentation here.
• docs/_static/css/toggle.css is the stylesheet for the toggle button.
• docs/_static/css/dark.css is the stylesheet for dark mode. The syntax highlighting
• docs/_static/js/toggle.js is the JavaScript that implements the toggle. Initially the docs are displayed using the default ("day") style. On the first toggle, dark.css is loaded and applied. The active mode is stored in localStorage so it will persist across sessions.
• in docs/conf.py, some settings are modified to ensure all of the above files are included when rendering. I removed app.add_js_file in favor of html_js_files - same effect, less LOC.

Formatting

• Fix some code highlights that were implemented with markdown syntax (single backtick) instead of RST (double backtick). In RST, these render as italics.
• In docs/web3.parity.rst, replace tabs with spaces in some code blocks. The mix of tabs and spaces together was making the blocks render strangely.
• Fix broken link in docs/ethpm.rst - it was missing a trailing underscore.

Example

• To see the toggle mechanism in action, visit the Brownie documentation.
• The syntax highlighting is using Monokai as implemented by Pygments:

Todo:

• Add entry to the release notes

Cute Animal Picture

[kclowes]

I think we want to leave this in?

[iamdefinitelyahuman]

I didn't remove it, I'm just handling it using html_js_files instead of app.add_js_file. Both have the same effect, but html_js_files accepts multiple paths so it seemed more efficient.

Related documentation:

• app.add_js_file
• html_js_files

[iamdefinitelyahuman]

Happy to change it back though if you prefer.

[kclowes]

Ah, interesting. The new way works for me!

[kclowes]

Thank you @iamdefinitelyahuman! This is awesome!

[pipermerriam]

post-merge feedback

@iamdefinitelyahuman have you considered releasing this as a stand-alone sphinx RTD theme?

[iamdefinitelyahuman]

@pipermerriam I hadn't, but I am now :)