Refactor doctools marketing pages

[ericholscher]

We want to use the doc pages as SEO for queries like "hosting mdbook", so we should refactor the website doctool pages to note that we support any tool, and have some good examples of configs and live projects using those tools (with test-builds as a backup).

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Now, I feel that we are repeating ourselves by having a "marketing page" and a "documentation page" for every tool. I think we should think a little more about this to avoid this repetition.

We should highlight all the features that Read the Docs adds on top of any documentation tool here with nice copy, images and GIF examples in the marketing site with a list of all the supported doctools pointing to our specific documentation pages. This will simplify the maintenance and also show why Read the Docs is different than a regular hosting providing, promoting what we want to promote: our specific features.

What do you think?

Originally posted by @humitos in #336 (review)