Improvements based on accessibility feedback

[richtabor]

The only noticeable change is that the archive template will now render the title of the archive (the tag, category, etc) and the description (if there is one added to the tag, category, etc).

Feedback reported:

1. The site title is incorrectly marked as an H1, which results in
   multiple H1s on pages and posts.
   <h1 class="wp-block-site-title" data-element-id="headingsMap-0-0"><a href="https://reverent-cod-7b24ca.instawp.xyz/" target="_self" rel="home ">[wp-a11y-theme-test.instawp.xyz](http://wp-a11y-theme-test.instawp.xyz/)</a></h1>
   This should be marked as a paragraph rather than an H1 so that the post
   title is the only H1 on the page.

2. The "You may also enjoy..." text on single posts is not marked as a
   heading, though it should be and the blog posts below it have the
   incorrect heading level set. This text should be an H2 instead of a paragraph and the blog posts below
   it should be H3s instead of H2s.

3. The H1 on tag and category archive does not match the purpose of the
   page. It stays as the hard-coded "Hi, I’m Rich Tabor" text. This should output the title of the category or tag.

4. Color contrast failures:
   The color #7A7A7A on a white background has a contrast ratio of 4.3:1 and
   fails contrast checks.