Log Message:
(devel/R-fs) Updated 1.6.4 to 1.6.5

# fs 1.6.5

* `path_ext()` and `path_ext_remove()` return correct extension and
  path, respectively, when multiple dots are present in file name
  (@IndrajeetPatil, #452, #453).

* `path_rel()` provides an informative error message when multiple
  starting directory paths are specified (@IndrajeetPatil, #454).