Changed description, added more details on package functioning.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@240 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added detail on call to 'lm'.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@241 edb9625f-4e0d-4859-8d74-9fd3b1da38cb