Introduce --key option for using your private key instead of a passphrase.
Improved private-key mode: list all available keys and ask user to select.
Merge branch 'master' into private-key
Merge branch 'master' into private-key

Conflicts:
	bin/vault
Only boot readline if needed, since it interferes with pw.
Little formatting tweaks.
Merge branch 'master' into private-key

Conflicts:
	bin/vault
	package.json
Docs for the --key option.
Correct a typo.
Add new Node versions to travis.yml.
Support saving key selection to the .vault file.
Refactor: one function for selecting a public key, another function that takes a public key and signs a value.
Document how to save a private key setting.
Make the --phrase flag override a stored --key setting.
Merge branch 'master' into private-key
Merge branch 'master' into private-key
Completion scripts don't need to be executable.
Merge branch 'private-key'

Conflicts:
	node/cli.js
	package.json
	spec/node/cli_spec.js