3.0.0: Fragments

• Heads up: Dropped compatibility with xp-forge/handlebars versions
  lower than 9.1.0
  (@thekid)
• Merged PR #15: Implement fragments, which can thought of as "instantly-
  invoked inline partials".
  (@thekid)
• Merged PR #14: Make it possible to pass fragments to the render() and
  write() methods. This will select an inline partial and render that
  instead of the whole template.
  (@thekid)