Added complete access to the pivotal engine via R for all supported distributions (2-dimensioned) with options.  No need for abrem to make .Call into RcppArmadillo code.  abremPivotals should simply be a depend of abrem.  Man pages need expansion of details and value sections.  Testing is still in progress.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/abernethy@90 edb9625f-4e0d-4859-8d74-9fd3b1da38cb