Fix piping to jsonpath at command line 

I couldn't get piping from STDIN to work at the command line at when I checked the code I couldn't see how it could work because it seems to parse the input one line at a time. If the JSON spans multiple lines then it means the parser is only being applied to the JSON fragment from a particular line rather than the whole file. I can only think it was tested against a JSON input that was all on one line. 

This change fixes it to work with a multiline JSON file.