Cleaning up EWMA code and adding more functionality for EWMA estimates

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@116 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
First draft of vignette for estimating correlations and volatility

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@117 edb9625f-4e0d-4859-8d74-9fd3b1da38cb