Address referee #1 feedback about section 4.

Answer many of the specific questions from the referee: Why use S4 and
not RC (answer: written before RC availalbe, acknowledge that RC would
be better). objects made mutable by usual functional copy on modify
semantics in mutation methods, avoid pseudo-method.

Fix typographical issue with subheadings.  Make it more concise with
\subsection* and combine a few.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@900 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Remove tables 3-8 with full slot and method descriptions for each
class in RProtoBuf.  This belongs in the documentation, not the paper.
Refer the reader to the full docs once at the beginning of this
section and remove all the references to tables in each subsection.
Further minor edits are needed here.  This was suggested by referee
#1.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@901 edb9625f-4e0d-4859-8d74-9fd3b1da38cb