QuantLib SWIG bonds example for R

Luigi,

Here is a first pull request based on the commit 'Modeled after bonds.py which it replicates'

I am not entirely sure I got my branching right (spurious 'remotes/origin' in 'remotes/origin/R01030x-branch') but this is a single file that will do no harm -- it should work with Joe Wang's R/SWIG module as is, and I have future improvements to that.

Dirk