Integrate & blog about 'sign-machine'; ability for a post to add a 'footer-script'

[nfreear]

..

• [ ] ~ Blog post, sign-machine repository ~ https://github.com/nfreear/sign-machine
• [ ] ~ A proposal for an x-footer-script property in the YAML front-matter for a post/ page ...
• I should document all the custom front-matter properties !!

---
layout: post
title:  Sign-machine rebooted
date:   2017-05-22 17:23
# ...
x-footer-script: https://cdn.rawgit.com/nfreear/sign-machine/2.0-alpha/src/sign-machine.js
---