Add yaml verification — closes #20

[matthew-andrews]

The problem with this is it effectively forces js-yaml to be a dependency of every single one of our repositories (because we have circle.ymls).

What do you think?

[wheresrhys]

I'd exclude circle.yml.

You could write a hacky yaml verification lite by checking for inconsistent whitespace, which is the most common mistake

[matthew-andrews]

Maybe we could use something like this:-
https://github.com/paazmaya/yaml-validator

And then we could have a .yaml.config.js file to look for which would mean projects could opt into it.