Creating lots of small objects frequently can drastically decrease
performance.  This commit introduces three fixes which avoid this:

- Use a preallocated palette and indexed-to-rgb destination Typed Array
  (the destination typed array is currently allocated at `4 * width *
  height`).

- Inline `getTightCLength`, which returned a two-item array.

- Pass RGBX data directly in a Typed Array to the Display, which
  avoids an extra loop, and only creates a new Typed Array View,
  instead of a whole new ArrayBuffer.