Merge from vendor branch TNF:

Merge from vendor branch TNF:
RRD::Simple provides a simple interface to RRDTool's RRDs module.
This module does not currently offer fetch method that is
available in the RRDs module. It does however create RRD files
with a sensible set of default RRA (Round Robin Archive)
definitions, and can dynamically add new data source names to an
existing RRD file.

This module is ideal for quick and simple storage of data within
an RRD file if you do not need to, nor want to, bother defining
custom RRA definitions.