Skeleton WKNNF class

* just the constructor/destructor
functional implementation of query
fix: must call build_tree

* in case it was not built on init
simplify preparing results for R
refactor with private queryF method

* this will work directly on points in MatrixXf with 3 rows
Add queryWKNN method

* direct search with points in another WKNNF object
* need not be one that has float data
enough docs for the class to be exported
import methods

* for WKNNF class
add kcpoints dataset for tests
oxygen for import methods
add getPoints() method

* could make this a read-only property?
make WKNNF return a RANN::nn2 like list
Add tests for WKNNF
Merge branch 'feature/WKNN'

* feature/WKNN:
  Add tests for WKNNF
  make WKNNF return a RANN::nn2 like list
  add getPoints() method
  oxygen for import methods
  add kcpoints dataset for tests
  import methods
  enough docs for the class to be exported
  Add queryWKNN method
  refactor with private queryF method
  simplify preparing results for R
  fix: must call build_tree
  functional implementation of query
  Skeleton WKNNF class