version date      description
0.1     07/19/12  The first version on CRAN
0.2     09/27/12  The second version.  Fixed a bug in the ATE CBPS.
0.3  	01/18/13  The third version.  Updated the ATE variance estimate.
0.4     03/30/13  Adds function for fitting marginal structural model.  Fixed standard error in cross-sectional case.
0.5 	05/07/13  Adds function that handles three- and four-valued treatments.
0.6 	06/05/13  Adds multiple binary treatment case, as well as extending plot and summary capabilities.
0.7     07/24/13  MAJOR BUG FIX.  In versions 5 and 6, CBPS for the cross-sectional case interprets 1 as untreated and 0 as treated.  This has been fixed.
0.9		08/07/14  Adds CBPSContinuous.  Major changes to interface for and backend of CBMSM.
0.10	09/07/15  Adds nonparametric estimation.  Simplifies CBPS output.  Numeric treatments now interpreted as continuous, and factors are interpreted as multi-valued.  Improves interface for ATT.
0.11	04/29/16  Adds Improved CBPS from Han et al through the baseline and diff arguments.
0.12	11/01/16  Fixes bug that affected the weight for the first observation in the continuous case.  Fixed bug that caused npCBPS to ignore choice of corprior.  Added SVD to CBPS Optimal.
0.13 	12/27/16  Fixes bug for CBPSOptimal, changes balance conditions for CBPS Continuous, and fixes issues with covariance matrix of coefficients.