Client docs: TSDoc API generator not working

[peggyrayzis]

For the Apollo Client docs, we use TSDoc to automatically generate API docs. Currently, they're not showing up in the Client docs: https://5c7dc06c86dd760008a87e71--apollo-client-docs.netlify.com/docs/react/api/apollo-client

[peggyrayzis]

• Change the color of the teal inline code to body copy
• Change the styling of the heading so it is consistent with the uppercase styling on the left hand nav
• Match the grey fill behind the banner to what we have in the code block
• Round the corners to match the border radius of the code block
• Make the line height consistent with what we use elsewhere
• Sitewide: remove default underline on links, show underline on hover unless it's inline code (which should be default underlined in pink)
• Fix backticks in headings (React Apollo API docs)

[trevorblades]

Fixed by c2bde9e and 5aea35c