0.4.0 release candidate

[pablothedolphin]

Did a hell of a lot of stuff in this one:

• GameObjects are spawned with their name set to the object type.
• Complete reconstruction of layer hierarchies is now a thing.
• Meshes, lines and curves can be scaled using an exposed scale factor property in the manager.
• Manager class has add and remove methods exposed for controlling the receiver list.
• Manager class has an enum which helps control how quickly streams are spawned in.
• Added an editor script which allows users to create an instance of a SpeckleUnityManager in the scene without the use of prefabs.
• Wrote XML comments for most of the API. All important bits are well documented.
• Generated docfx documentation site under the docs directory which only has scripting api docs at the moment.