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
We were passing arguments in the wrong order to PBKDF2. Fix, and provide postinstall instructions for migrating your .vault file.
Only generate a password if the service and phrase fields have text in them.
Display generated password in a fixed-width font.
Remove an unused variable.