Basic implementation of WANN using Rcpp module

* this produces a reference class, WANN, that contains an ANN tree + the points
* with a bit of work this could be the basis for a faster implementation of
  nearest neighbour searching when reusing points (by avoiding re-building tree)
* could also save some space by using floats
implement a WANN querySelf method

* on the way to making a method where you can query one WANN object with another
import all of Rcpp
Add getPoints() method to return R matrix

* not very fast ...
* I have a feeling one could just copy directly since they are both row oriented
Add public queryWANN method

* see http://romainfrancois.blog.free.fr/index.php?post/2012/10/25/Rcpp-modules-more-flexible
* not sure if RCPP_EXPOSED_CLASS is really still necessary
* note that this must be called as follows:

  w1$queryWANN(w2$.CppObject,1,0)

* probably I should provide a method somewhere that ensures that can cope with
  the object itself.
* spent a lot of time trying to figure out why this doesn't work:

  w1$queryWANN(w2,1,0)

(it crashes the R session)
getPoints method should be public
STY: cpp whitespace
STY: more code tidying

* tabs to 2 spaces
* no functional changes
queryW->queryANN

* and remove superfluous WANN* queryW method
Define ANN_COORD_TYPE and ANN_DIST_TYPE macros

* can be used e.g. in makevars
Make building the tree optional
add delete_tree method
export the build and delete_tree methods
rstudio: spaces for tabs
Add some tests and test data (in data)
Document sample data
Depend on R>=3.0 and methods

* methods package needed for WANN reference class
Update README to include WANN details
Merge branch 'WANN'

* WANN:
  Update README to include WANN details
  Depend on R>=3.0 and methods
  Document sample data
  Add some tests and test data (in data)
  rstudio: spaces for tabs
  export the build and delete_tree methods
  add delete_tree method
  Make building the tree optional
  Define ANN_COORD_TYPE and ANN_DIST_TYPE macros
  queryW->queryANN
  STY: more code tidying
  STY: cpp whitespace
  getPoints method should be public
  Add public queryWANN method
  Add getPoints() method to return R matrix
  import all of Rcpp
  implement a WANN querySelf method
  Basic implementation of WANN using Rcpp module
Fixes and tests for nn2 input for non-matrix data