clean up serialise

expose the api functions as desired, and hide the non api functions
(avoids name spacing issues)

this exposes a nice little function kowhai_str_to_path() to essentially
de serialize a path which is quite useful (its counter part to serialise
a path exists, but is not exposed as I am not sure it has much use at
this time)
Merge pull request #6 from othane/node_serializer

clean up serialise