Changes for v.0.1 : First version. IKbandwidth, DCdensity and RDestimate created and working. 
Changes for v.0.2 : Added separate function for kernel weights, S3 methods for plotting and summarizing RD objects. 
Changes for v.0.21: Fixed bug in RDestimate when frame=TRUE and no covariates. 
Changes for v.0.22: Fixed handling of missing values. 
Changes for v.0.3 : Improved plot method, fixed some various bugs.
Changes for v.0.31: Added plot.RD documentation. 
Changes for v.0.4 : Made compatible with CRAN. 
Changes for v.0.41: Fixed submission issue. 
Changes for v.0.42: Submission issue. 
Changes for v.0.50: Added better error messages. Fixed bug in plot.RDD. Other minor code changes. 
Changes for v.0.51: Fixed a bug which resulted in crashes of the summary.RD and plot.RD functions. Big changes in the handling of bandwidths. Now accepts a vector of bandwidths as inputs. Some outputs have been modified to reflect this change.
