Add support for asymmetric encryption and gpg-agent

[akheron]

Things to think about first:

• Should we support multiple recipient pubkeys?
• Should we have a pubkeyring for the password store so that encrypting is always possible?
• Should we support both asymmetric and symmetric encryption in the same password store?

[egh]

I've added support for this to my fork. If you set the keyid config param, sala uses your public key to encrypt the master password. It works for me, but all I really wanted from it was to let gpg-agent handle my password so I didn't have to type it all the time.

[akheron]

Interesting. What happens if gpg-agent is not running? I assume it just fails because the --batch and --no-tty flags are passed to gpg.

[egh]

Yes, unfortunately. I guess I could check & prompt for a password if it fails.