Port functions to the 'modern' puppet function API

[alexjfisher]

This module contains two functions, (ensure_prefix and to_hash_settings), written in the old/legacy lib/puppet/parser/functions API. We should port these to the 'modern' function API.

An automated PR for this was created back in #561. This could be picked up, but it's probably equally easy to implement from scratch.

[yakatz]

Should that PR also remove the old functions?

[alexjfisher]

Yes, probably. I've made a start on this. Will open a PR soon.