fix .html suffix on generated urls

[cwaring]

Originally posted by @cwaring in #154 (comment)

The first chunk of 404s are caused by this upstream issue in VuePress, we recently introduced local 404 checking for internal content urls #119, which requires the links to point to the .md version of the file and unfortunately it seems that the markdown link generator is hardcoding the .html suffix.

A couple of solutions to this:

1. Patch VuePress upstream to fix this issue so that it interacts with the clean url plugin better.
2. Revert back to using absolute path links in our docs and then do 404 checking async via another external crawler (could be more comprehensive).
3. Remove the clean urls plugin and default to .html extensions for our docs.

The later broken links are related to how your browser refetches these metadata files on route change. These paths are relative in order to be compatible with IPFS gateway links (gateway.ipfs.io/ipfs/hash/) and if you open the page in a new window you will see the paths are correct on first load. I would like to find a better solution to this but it's a lower priority, but as we are currently not hosting these docs on IPFS (due to required server-side redirects) I could disable this for now.

[cwaring]

This is now an upstream fix for this issue. TODO: test and report back using our docs configuration.