Moved the rendering of a template to new func

this takes as an argument a StringSink
Better call method implementation

we now return the response of the call based on it's input
arguments. If we've been given a StringSink use it and return
it, otherwise return the string representation of our rendered
template
Allow a StringSink named paramter to render funtion
The output of the result function is not always String
Added failing test for #12
Fixed failing test (NPE)
Merge branch 'issue12'

fixes #12