Define a standard output format for all release docs

[oubiwann]

Part of epic #28

[oubiwann]

My guess is that we'll want to start with HTML ... that would require testing LFE with pandoc HTML output. We already get HTML for free with lodox, so libraries would be covered with this approach.

Once lodox has support for EDoc, part of the docs build process for running lodox against LFE could including all the LFE .md source docs as lodox topics, so that we could simply use the lodox interface for all LFE docs.