Update gosteno

$ git shortlog 0bec89c5..949de95e
Jeff Li (3):
      Update the demo in the document
      Rename  steno-prettify to gosteno-prettify
      Give more detail about gosteno in the documents

Pieter Noordhuis (5):
      Add source field to log record
      Add pid field to log record
      Remove util.go
      Less verbose variables
      Use lowercase field names in JSON codec