Remove a duplicate word in the last paragraph of the introduction, add
a word to fix a linewrap in section 4, and add a paragraph to the
beginning of section 7 to make it more interesting.  More work on
sections 6,7, and 8 is sorely needed.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@903 edb9625f-4e0d-4859-8d74-9fd3b1da38cb