(lang/R-cpp11)  Updated 0.2.7 to 0.3.1

# cpp11 0.3.1

# cpp11 0.3.0

## New functions and features
* New `x.empty()` method to check if a vector is empty (@sbearrows, #182)
* New `x.named()` method to check if a vector is named (@sbearrows, #186)
* New `na()` free function to return the NA sentinels for R objects
  (@sbearrows, #17 9)

## Major fixes

* Memory no longer inadvertently leaks when move constructing vectors
  (#173)

## minor improvements and fixes

* Incorrectly formatted cpp11 decorators now output a more informative
  error message (@sbearrows, #127)
* Generated registration code now uses C collation to avoid spurious
  changes from `tools::package_native_routine_registration_skeleton()`
  (@sbearrows, #171)
* Makevars files which include filenames now handle spaces in paths
  properly (@klmr, #160)

(mef)