CSS updates: ul and pre elements

Polish Configurator section

Adjust the H2 and H2 margins

reduce the line-height of the sidebar

rearrange the sidebar a bit

limit the TOC to H1 and H2

remove line drawing chars

make custom_keycode_names.md a faq entry instead

reduce space on h3s

break feature_advanced_keycodes.md up into multiple files

improve our docsify setup

fix numbering

overhaul the newbs guide

More sidebar organization

Add API documentation

update flashing.md

- minor typo on intro paragraph (the -> them)
- remove note about :check-size target (`make` task now does this automatically)
- heading level for Caterina commands section
- typo regarding Halfkay (come -> comes)

update newbs_building_firmware.md

Update the text sample for when the compile task completes.

Rework the newbs guide around the qmk cli

Add dark mode support

_summary.md: move Auto Shift page to Software Features category