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/exploring.md

@@ -0,0 +1,33 @@
+# Exploring Archived Content
+
+The ReplayWeb.page homepage lists an index of all your loaded archived items. Items are searchable by their title or source, and can be filtered by the date they were loaded or their title.
+
+## Navigation
+
+ReplayWeb.page's sidebar is the fastest way of finding content within an archived item. It features several tabs that allow information to be accessed:
+
+### Page
+
+The pages view lists all the webpages stored within the archived item.
+
+#### Searching For Pages
+
+Pages can be searched for by their title, URLs, or extracted text if available.
+
+ReplayWeb.page will load pre-generated full-text search data when loading WACZ files, and will also attempt to generate full-text index from HTML files contained in WARC files upon loading a WARC.
+
+### Resources
+
+The resources view displays all the content within a loaded archived item, listed by URL and media type. For many archived items with no page or curatorial metadata available, this is the best way to explore the archived contents.
+
+This view is available for all archives that only store raw data.
+
+#### Searching For Resources
+
+Page resources can only be searched by URL. Searches can be performed by exact URL, by URL prefix, or by searching for any string contained in the URL.
+
+The _URL Prefix_ option is best for searching large archives that require on-demand loading. The _Contains_ option will not find any URLs that have not yet been loaded.
+
+### Story
+
+The story view presents lists of curated pages and a description of their significance, as specified by the creator of the web archive. This option is only shown if there is a curated story. As curated lists are not a standardized part of the WARC format, only WARCs exported from [Conifer](https://conifer.rhizome.org/) can be configured to use this option.