docs/theme-configs

[alphasentaurii]

Docs Configuration changes:

• use furo theme
• update logo images
• add new subproject urls to intersphinx_mapping
• add "sphinx.ext.extlinks" to extension list
• use monokai pygments style for code formatting
• override html_sidebars (incompatible with furo theme)
• fix copyright text in footer
• update project url
• custom graphviz settings to render diagrams properly in dark mode
• use abbreviated version format in sidebar heading (html_title)

Docs Content changes:

• delete intro.rst page and remove from TOC (content moved to main website's overview.rst page)

[braingram]

How about we turn this into a link to https://www.asdf-format.org/en/latest/overview.html?