0.6.0

• Improvement - content_type and field are moved into ProceedingMeta model from Transition model. This requires to migrate 0002. This migrations will move value of the fields from Transition to ProceedingMeta.
• Improvement - Slug field is added in State. It is unique field to describe state. This requires to migrate 0002. This migration will set the field as slug version of label field value. (Re Opened -> re-opened)
• Improvement - State model now has natural_key as slug field.
• Improvement - Transition model now has natural_key as (source_state_slug , destination_state_slug) fields
• Improvement - ProceedingMeta model now has natural_key as (content_type, field, transition, order) fields
• Improvement - Changelog is added into documentation.