Add support for keypairs

Adds support for the following keypair operations:
- ListKeyPairs yields the list of available keypairs.
- CreateKeyPairs will create or generate a new keypair.
- DeleteKeyPair wil delete a keypair.
- ShowKeyPair will yield the named keypair.
Add PrivateKey field to KeyPair for returning from CreateKeyPair
Merge pull request #78 from markpeek/markpeek-keypair

Add support for keypairs