added zzz.r file - with code to override dendextend functions in case dendextendRcpp is loaded AFTER dendextend.
cut_lower_fun function added - allowing for a faster cutree(h) for dendrograms!
Version bump to 0.3.0

Also updated the authors list per Romain's request.
Change SEXP to RObject

Also changed file name from cut_lower_labels.r -> cut_lower_fun.r
Rcpp_cut_lower now changes the output of the nodes to be of dendrogram class
      which enables the fast operation of functions on them!
Copying the object to avoid strange behaviors within R!