Add a 'server' mode (embedded test http server) to serve pages when writing

[ajkavanagh]

This is pretty standard faire: enable running in a mode where the site is served locally so you can view pages whilst writing them and 'see' the site without actually having to deploy it. Key features:

• NOT for production use. i.e. this is a test server for one user to access individual pages.
• Watch for changes in the directory
• Enable live reload on changes.