v0.3.0

This release fixes a couple of missing elements:

• The v3 high-level Document object was incorrectly implemented. The security property needed to be a slice. Breaking
• Server was missing extensions in both high and low-level APIs.

This is a whole feature bump because of the change to the Document model. security is now a slice, not a single instance. A small breaking change, but a breaking one none-the-less.