Adding VaR backtesting functions

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@132 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Adding demo for VaR backtesting. Fixing bug in bootstrap VaR backtest

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@133 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Making forecast a generic function for EWMA and GARCH models. Adding script for quantifying vol

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@134 edb9625f-4e0d-4859-8d74-9fd3b1da38cb