Add upgrade command.
Do not include bootstrap dependencies.
Add s, f and dash as bootstrap dependencies.
Add outdated command.
Remove Casks dependencies in subprocess created in step.
Remember load paths for nested calls to epl-initialize
Do not implicitly initialize EPL
Error on dirty tree on upgrade.
Merge branch 'bootstrap-dependencies' into v0.5-wip
Use s-present? instead of s-presence.
Merge branch 'upgrade-command' into v0.5-wip
Merge branch 'more-bootstrap-packages' into v0.5-wip

Conflicts:
	cask-cli.el
Fail occurs when requiring s.
Update Travis Cask url.
Error message have changed in snapshot.
Bootstrap EPL instead of keeping a local copy.
Remove Carton deprecations.
Small refactoring using -when-let.
Use new API for f-write.
Add instructions for how to upgrade Cask in README.