Metaframe editor

User docs: ./public/README.md Developer docs: ./README-developer.md

Test in these places (replace editor.mtfm.io with the local dev host):

• https://app.metapage.io/dion/python-interactive-plotting-5d2893f82bc94e7e8528a71c7693f2d0?view=default
• https://github.com/metapages/metaframe-js