Log Message:
(math/R-stringdist) Updated 0.9.12 to 0.9.15

version 0.9.15
- Fixe issue with zero-length 'nthreads' argument in all exported functions
  with this parameter. (Thanks to Brian Ripley for the notification and pointer
  to the problem)

version 0.9.14
- Fixed issue with zero-length strings in 'qgrams' (Thanks to Brian Ripley
  for the notification and pointer to the origin of the problem)