0.5.0

New features

• Usr: Added some more documentation on shell auto-completion. [Bart
  Verhagen]
• Usr: Added Bash and Zsh auto-completion support. [Bart Verhagen]
• Usr: Changed copyright in the documentation to the BSD 3-clause.
  Upgraded the end year of the copyright to this year. [Bart Verhagen]
• Usr: Added the custom plugins as a major way to do more advanced
  workflow optimization. [Bart Verhagen]
• Usr: The PWD environment variable is set to the actual working
  directory of a task. [Bart Verhagen]
• Usr: Added documentation on writing custom plugins. [Bart Verhagen]
• Usr: Added --list-plugins option for listing all available plugins.
  [Bart Verhagen]