1.0.0: New feature: public keys, add multiple keys.

Breaking changes:

• Input ssh-key renamed to ssh-private-key

New feature:

• Added ssh-public-key input. Allows adding remote host identities to known_hosts.
• Ability to add multiple public and private keys.
• When action is used multiple times, checks to see if ssh-agent is already running. Does not start a new agent if one is already started.