Specs update

[merc1er]

• The bulleted lists aren't indented (in fact they seem to stick left into the margin), is it possible to make them indented, and sub-bullets indented even more?
• I'm not sure what you mean about the specs submenu, but the menu at the top is still screwed up (eg, clicking on "Start Here" leads to a non-existent page).
• The relative links don't work, for example, look at /spec/2019-11-15-upgrade.html and the links to the other parts of the spec. It turns the links into links to .md files that don't exists (eg. /spec/2019-11-15-schnorrmultisig.md)
• For the menu with the May 2019 specs, could you just change the order so that the "Network Upgrade Specification" is first? this is the overall spec, so it should always be first first.