v0.3.0

• New: vidscroll/core, the plain JavaScript controller behind the React
  component (experimental).
• New: <vid-scroll> and <vid-scroll-section> custom elements for pages
  without React, plus a standalone CDN build (experimental).
• react is now an optional peer dependency, so non-React projects don't need
  it.
• Fixed: time-based sections briefly showed at load before the duration was
  known.
• Fixed: the video could freeze after two animation frames with the same
  timestamp.
• Fixed: an active section blocked clicks on content behind its empty area.
• ScrollVideoApi gains addSection and removeSection.