improved man page.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/recommenderlab@96 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
updated structure of recommenders and man page

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/recommenderlab@97 edb9625f-4e0d-4859-8d74-9fd3b1da38cb