Launch Unicorn as the runner user (defaults to "app").

In addition to launching Unicorn, the runner user must:
- delete the pidfile (since that user made it)
- send kill -0 to test the process
- kill Unicorn
Change variable to `unicorn_user`.

Don't require `use_sudo` to be true because that has wide-ranging
side-effects on the rest of the Capistrano script. Instead, since sudo
is required for running as a different user, just use `sudo` instead of
`try_sudo`.

Don't fall back on `runner` variable. If someone wants it to be the same
as `runner` they can just set it to be the same.
Merge pull request #43 from BMorearty/try-runner

Ability to launch Unicorn as a different user than the deployer
Added duplicate_unicorn method and task

Added duplicate task to tasks list
Merge pull request #42 from danielkman/master

Add unicorn duplicate task
adding configurable roles
version change
Adding the ability to declare which capistrano roles will run unicorn tasks. Useful for multistage deployments which have dedicated server behavior
merging conflicts with rebase