Rename project from Carton to Cask.
Use f function instead of native.
Can run both cask and carton command in steps.

 - When I run cask "..."
 - When I run carton "..."
Add migration information in README.
Quote keywords in deprecation warning.
Make sure we don't get output from previous buffer.
Set output/error to empty string for comparison.
Support old Carton file, but with migration warning.
Print output/error unless blank.
Allow old elpa directory.
Favor .cask over elpa if both exists.
Add note about relevant files to update.
Force users to rerun cask.

Previously, the old `elpa` directory was used if it existed. This is
bad for many reasons, one is because we now support multiple versions
of Emacs.
Add one more migration step.
Update some URLs.
Merge branch 'from-carton-to-cask' into v0.4-wip
Skip quotes in commander block.