1.6.0

Added

• PID of last executed task to job struct
• Credo code linter (only for dev and test)
• Total downloads badge to README
• Elixir 1.1.0 and Erlang 18.1 to Travis-CI config

Fixed

• Max hour is 23, not 24
• Long-running jobs could overlap
• Typo in README (Lucas Charles)
• Incorrect function and response types in readme (Bart van Zon)
• Unnamed job tuples cannot take args (Lucas Charles)
• Job names can only be atoms and can't be GC (Luis Hurtado)