React Router should handle internal page links generated in markdown

[paulathevalley]

The markdown renderers turn links into <a> tags, which naturally are not handled by react router. If they are links to internal pages, they should be intercepted and handled by react-router. If they are relative links, they should work both on github.com and on the dox site.

• [ ] For relative links to work on both github and the dox site, some adjustments need to be made to the paths. For example, github might link to ../guides/other-guide.md whereas the dox site equivalent would be ../../guides/other-guide/ , see example implementation on formidable-playbook-docs.
• [ ] Next, to prevent a full page reload of internal pages, the <a> links need to be intercepted and handled with react-router, see example implementation on spectacle-docs.