v0.6

New features

• Add pipeline function to support expression-based pipeline evaluation. (#60)
• Piping to string now cat the string in the console. (#61)
• Question mark now supports binary operation ("message" ? expression) in which
  expression is evaluated while "message" is printed ahead of its value. (#62)

Improvements

• <<- and ->> now correctly perform global assignment in enclosed expression in
  a pipeline. (#65)