Add Cloudfront and ElasticBeanstalk support

[kageurufu]

Refactor Certificates into AWSCertificate sub-classes,
allowing for the easy adding of new listener providers
in the future. CloudFront and ElasticBeanstalk are both
implemented this way. Fix #41

Also, add the --cert-only flag, fix #13

This PR supersedes #44 and partially #17

[alex]

FYI, I plan to review this this weekend.

[hayd]

bump!

[holyjak]

Hello, what is the status of this? What is it that does not work w.r.t. Elastic Beanstalk? Thanks!

[kageurufu]

It works perfectly for me, I'm using my fork in production for two seperate environments on AWS.

[hayd]

@kageurufu Could you share anything about your configuration? Searching this repo for elasticbeanstalk doesn't suggest it's implemented - did you have to hand write this?

Edit: Oh, I see you said "my fork", sorry for the noise. I still think this would be good to include.

[kageurufu]

@hayd: If @alex wants it, he's welcome to integrate my changes. Last I used it, this still worked, but I've since just switched to ACM, for ease of maintenance.

I only closed this to clean up my open pull requests, as it's been nearly 3 years since the last discussion