rename package to nabor

* don't know how I missed it the first time ...
Merge branch 'master' of github.com:jefferis/nabo

* 'master' of github.com:jefferis/nabo:
  don't format citation as R code
  comparison with RANN, thank Rcpp* people.
  Update README.md

Conflicts:
	README.md (due to nabo renaming)