v0.3.1

• Fixed: easing presets moved the video backwards near the end of the scroll.
  All presets now move forward only.
• easing and smoothingTauMs apply immediately when they change; a new
  fps rebuilds the scroll mapping; a changed optimize value reloads.
• vidscroll/core: update() now changes only the options you pass, and the
  new setOptions() replaces all of them.
• fullPreload={false} checks the URL too, and an invalid length goes to
  onError instead of throwing.
• The error message is shown even with a custom loader.
• CLI: --fps is a cap: slower sources keep their frame rate.