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/user-guide/index.md

@@ -0,0 +1,28 @@
+# User Guide
+
+## Getting Started
+
+1. Check out [Loading Archived Items](loading.md) to point ReplayWeb.page towards the file you wish to view.
+2. Once your file has been loaded, [learn how to navigate the archived content](exploring.md)!
+
+## Supported Formats
+
+While ReplayWeb.page aims to support a variety of formats for archived web content, for best performance we recommend using WACZ files. To archive webpages to WACZ files on a per-page basis, we recommend [ArchiveWeb.page](https://archiveweb.page). If you need to archive entire websites, check out [Browsertrix](https://browsertrix.com).
+
+??? question "WARC?  WACZ?  What's the difference?"
+    Due to the nature of the WARC format, the entire file must be read on first use to generate an index — a list of all the pages and content available in the file used by ReplayWebpage to rebuild and display the archived content.
+
+    Inversely, WACZ files are always loaded on-demand and no indexing is required. The initial archive view should load very quickly as a result.
+
+    For users comfortable with the command line, we recommend converting WARC files to WACZ files by using the `wacz` python library, see [py-wacz on GitHub](https://github.com/webrecorder/py-wacz) for more information.
+
+ReplayWeb.page supports the following file formats listed as "Supported". Format type is determined based on the file's extension.
+
+| Format  | Extensions          | Status         |
+|:--------|:--------------------|:---------------|
+| WACZ    | `.wacz`             |  <span class="status-success">:bootstrap-check-circle-fill: Supported</span>     |
+| WARC    | `.warc`, `.warc.gz` |  <span class="status-success">:bootstrap-check-circle-fill: Supported</span>     |
+| HAR     | `.har`              |  <span class="status-success">:bootstrap-check-circle-fill: Supported</span>     |
+| WBN     | `.wbn`              |  <span class="status-danger">:bootstrap-x-octagon-fill: Not Supported</span>     |
+| ARC     | `.arc`              |  <span class="status-danger">:bootstrap-x-octagon-fill: Not Supported</span>     |
+| CDX     | `.cdx`, `.cdxj`     |  <span class="status-success">:bootstrap-check-circle-fill: Supported</span>     |