Use R_registerRoutines to improve the efficiency of calling C++ routines; Rewrite the package documentation using roxygen2; Update file format

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/crf@19 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Add missing files

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/crf@20 edb9625f-4e0d-4859-8d74-9fd3b1da38cb