Add WKNND class based on WKNNF
tests for WKNND class
docs/exports for WKNND/F classes
remove knn1 function

* not really very interesting

remove knn1 tests
refactor knn(_brute) using corrected knn_generic

* this copies the data matrix on input, transposing it from Nxd to dXN
  (i.e. R convention to libnabo's convention)
* change interface/results to match RANN::nn2
update tests for knn functions
Update WKNNF/D tests to reflect new structures

* all tests relating to knn are still failing
give build_tree an optional treetype argument
Move definition of WKNND into header file
Use WKNND object to implement knn function

* this fixes all remaining test errors
* still not really sure why
Merge branch 'fix/knn'

* fix/knn:
  Use WKNND object to implement knn function
  Move definition of WKNND into header file
  give build_tree an optional treetype argument
  Update WKNNF/D tests to reflect new structures
  update tests for knn functions
  refactor knn(_brute) using corrected knn_generic
  remove knn1 function
  docs/exports for WKNND/F classes
  tests for WKNND class
  Add WKNND class based on WKNNF
fix compiler warning (comma ending enum list)

./nabo.h:284:24: warning: commas at the end of enumerator lists are a C++11 extension [-Wc++11-extensions]
                        TOUCH_STATISTICS = 1, //!< perform statistics on the number of points touched
Depend on R>=3.0

* for Rcpp 0.11.2
* also need R>=2.12 for sample data