ellipsis 0.2.0

ellipsis has officially graduated from experimental to maturing in the
package lifecycle.

• The main change of this release is that check_() functions now
  throw custom errors, rather than warnings.

• check_ functions have been optimised for the most common case of no
  problems. This means that you use it in more places without worrying
  about the performance cost.

• New check_dots_empty() that checks that ... is empty (#11).

• Improved error message suggesting that you check for mispecified argument
  names.