added show method

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/yuima@301 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added show method

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/yuima@302 edb9625f-4e0d-4859-8d74-9fd3b1da38cb