Move blog URL out of root

[maphew]

Publish blog to http://leo-editor.github.io/blog sub-folder instead of root.

Part of upstream leo-editor/leo-editor#480

Side effect is to simplify the publishing process: we don't need to manage 2 repo's anymore just to add an article.

• In GH navigate to Repo >> Settings >> Enable Github Pages to publish from ./docs folder in master branch.
• publish Content
• merge or discard mismatched content
• Erase blog content from other repo