Added requirements for 0.y.z versions

There is a lack of clarity of what the y and z releases do when following Semver.  Whilst it's appropriate to allow the API to change as it's stabilising, it's helpful to work within the framework to some extent.  Especially to ensure that the patch version doesn't completely change everything.

This change provides guidance on how to respect versioning in 0.y.z releases whilst preserving the ability to break APIs through this period.  It also allows a developer to get to groups with the processes prior to going to 1.0.0 (they are able to learn from any mistakes in the 0.y.z period).