MKDocs conversion (#278)

Closes #252, Closes #250

## Changes
- ReplayWeb.page uses MKDocs for documentation now!
- Requires both
[`mkdocs-macros`](https://mkdocs-macros-plugin.readthedocs.io/en/latest/)
and [`mkdocs-redirects`]
(https://github.com/mkdocs/mkdocs-redirects) plugins to be installed
- Redirects existing docs pages to their new locations under either
`/embedding` or `/user-guide`
- Unused images have been removed
- Adds new ReplayWeb.page branding!

All pages have received copy edits. All references to future (or
previously) planned features have been removed. More major content
changes of note are as follows:

### Supported Locations
- Made into a page, no longer a table. Locations are either supported or
not listed.

### Offline Use 
- Removes browser cache section, adds improved PWA install and uninstall
instructions.
- Removes navigation instructions to GitHub's releases section in favour
of a link

### Supported Formats
- Moved to the User Guide homepage
- Updated the format support

### Exploring Archives
- Example links for showcasing features have been moved to their
respective feature documentation section on this page

### Remove Usage, Examples, and Troubleshooting Pages
- Usage content is covered in the user guide index
- Troubleshooting content has been added to a question section on the
getting started page about WARC vs WACZ.
- Examples are now Featured Projects on the docs homepage!

### Build Process
- Removes Jekyll & related site assets.
- Adds new GitHub action for publishing
- Adds a python macro to dynamically load the replayweb.page version from package.json
- Relocates replayweb.page site content under /site (including docs)
- Some assets (favicon, logo) and sw.js/ui.js automatically copied into /site

---------
Co-authored-by: Ilya Kreymer <ikreymer@gmail.com>

site/docs/overrides/.icons/bootstrap/bug-fill.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-bug-fill" viewBox="0 0 16 16">
+  <path d="M4.978.855a.5.5 0 1 0-.956.29l.41 1.352A4.985 4.985 0 0 0 3 6h10a4.985 4.985 0 0 0-1.432-3.503l.41-1.352a.5.5 0 1 0-.956-.29l-.291.956A4.978 4.978 0 0 0 8 1a4.979 4.979 0 0 0-2.731.811l-.29-.956z"/>
+  <path d="M13 6v1H8.5v8.975A5 5 0 0 0 13 11h.5a.5.5 0 0 1 .5.5v.5a.5.5 0 1 0 1 0v-.5a1.5 1.5 0 0 0-1.5-1.5H13V9h1.5a.5.5 0 0 0 0-1H13V7h.5A1.5 1.5 0 0 0 15 5.5V5a.5.5 0 0 0-1 0v.5a.5.5 0 0 1-.5.5H13zm-5.5 9.975V7H3V6h-.5a.5.5 0 0 1-.5-.5V5a.5.5 0 0 0-1 0v.5A1.5 1.5 0 0 0 2.5 7H3v1H1.5a.5.5 0 0 0 0 1H3v1h-.5A1.5 1.5 0 0 0 1 11.5v.5a.5.5 0 1 0 1 0v-.5a.5.5 0 0 1 .5-.5H3a5 5 0 0 0 4.5 4.975z"/>
+</svg>