0.5.2: Improved markdown support and `index.src.html`

• escaping HTML code example from markdown template
• syncing features between <markdown> tag with readme.md template files, so they are rendered in the same way
• adding another template for specs and switching the official Spec filename to index.src.html

Special release for Living Style Guide driven development workshop https://github.com/sourcejs/workshop-lsg-driven-development.