Update documentation for v0.3.0

[bparks13]

Discuss the changes for version 0.3.0, but specifically the integration with SpikeInterface loading. This is related to #147, but I should confirm that any other changes made are properly reflected in the documentation.

There is already an active branch in the GUI docs to handle these changes: https://github.com/open-ephys/gui-docs/tree/onix-source-v0.3.0