404 for HIG docs - redirect old locations while updating major links

[jzacsh]

What Happened

Hitting 404s for HIG docs from prominent places (including first-party pages).

Expected Behavior

Get redirected from https://elementary.io/docs/human-interface-guidelines to https://docs.elementary.io/hig so the re-organization of pages doesn't matter to most anyone (it takes a long time to clean up old links).

Steps to Reproduce

See any of these places linking to HIG docs, which then 404:

1. "HIG" linked in https://blog.elementary.io/developer-tips-backgrounding-system-integration (found on https://islinuxabout.xyz/systray/)
2. huge "design" button centered on splash page of https://developer.elementary.io (found atop the elementary site)
3. web results for elementary os hig surface https://elementary.io/docs/human-interface-guidelines as the top result

Platform Information

web

[jzacsh]

(Not sure if this was the right place to leave this feedback, so until I hear back I'm just gonna pile any other findings here too)

• https://docs.elementary.io/hig/desktop-integration has a "Contractor" (fragment link intending to go to a different section of the same page?)
• toast page is empty: https://docs.elementary.io/hig/widgets/ui-toolkit-elements/toast