Version 0.1.3, 2019-04-22:

   More caution with PROTECT.

Version 0.1.2, 2018-03-26:

   Re-introduced two small changes to error checking accidently reverted
   in 0.1.1.

Version 0.1.1, 2018-01-08:

   Small changes for compatibility with new R Core REFCNT scheme,
   and for more caution with PROTECT.

Version 0.1.0, 2017-06-18:

   First version.
