Merge pull request #20 from oncletom/feature-promises

Promise-based interface
node-rsa key generation.
Merge pull request #22 from oncletom/sshkeygen-removal

Remove system ssh-keygen dependency
Travis + containers = <3
1.0.0
`crx.pack` now accepts the resolved content of `crx.loadContents`.
`crx -o` instead of `crx -f`
`crx --zip-output`