major version bump to 5.0.0

[joshbronson]

Ironfan v5.0.0 introduces the following new changes:

• plugins: Plugins allow Ironfan users to create custom components in order to group together related cookbooks and perform other arbitrary operations on clusters and facets.
• version pinning: Users can now list cookbook version dependencies in their components. These dependencies are used to generate a list of dependencies to be sent to Chef in the form of a Chef environment. This allows for a stricter pairing between versions of components, which provide most of the functionality of Chef roles (and much more), and Chef cookbooks.
• cluster diff: Cluster diff allows a user to compare the local configuration of a target cluster or facet against its remote manifestation.