Use YAML for eggs

[schrej]

Currently, eggs are exported in json format. Eggs can contain a lot of multiline strings, which makes it very hard to read them in json format.

YAML has much better support for multiline strings (see here) which would make it much easier to modify eggs as code and see changes in Pull Requests. In addition YAML is easier to read and we've converted wings to use yaml as it's configuration file format as well.

As YAML is basically an extension of JSON, it should be easy to be backwards compatible.

[parkervcp]

YAML is definitely easier to read and hand edit.

One thing we also need to consider is that we "should" be escaping all sentences as well. Any yaml specific catches all break parsing pretty hard.