[WIP] Add images

[BrunnerLivio]

Resolves #10

• Add image class

• Update documentation

• Extend test cases

• GET /1.0/images

client.images(true, (err, images) => console.log(images))

• POST /1.0/images
• GET /1.0/images/<fingerprint>

client.images(false, (err, images) => console.log(images))

• /1.0/images/<fingerprint>/export
• GET /1.0/images/<fingerprint>/refresh

client.images(false, (err, images) => {
    images[0].refresh((err, data) => console.log(data));
});

• /1.0/images/<fingerprint>/secret
• /1.0/images/aliases
• /1.0/images/aliases/<name>

[BrunnerLivio]

Currently, in the client class there is a method called client.create, which creates containers. Since you can also create images, it can be confusing whether you create a container or an image with the client.create-method.

I suggest changing client.create to client.createContainer and adding client.createImage.
This would be a breaking change.

Issue: #12

[alandoherty]

Looks good, only thing is the use of underscores vs camelCase which is inconsistent with some of the other classes.