Allow optional omission of CanvasMatrix.js

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl/pkg/rgl@1159 79a1b648-8b68-254f-b20b-c0b50f5137bf
Start on the vignette

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl/pkg/rgl@1160 79a1b648-8b68-254f-b20b-c0b50f5137bf
Mention rmarkdown

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl/pkg/rgl@1161 79a1b648-8b68-254f-b20b-c0b50f5137bf