Support the unity package manager

[lugehorsam]

As rightfully requested by @thegoldenmule

This mostly involved shuffling files around into a particular folder structure and creating assembly definitions for the Editor and Runtime bundles of our scripts.

Here's what it looks like in the package manager:

Closes #91

[lugehorsam]

I was looking for ways for the "In Development" label to not show up. As far as I can tell, unless the user downloads our package in UPM via the Asset Store, we will have that label. So that is a bit annoying but I am not sure if there's anything we can do about it. Obviously we'll still publish to the Asset Store so it'll go away if users use that flow rather than a git url.

[novabyte]

@lugehorsam Awesome. I have only a small follow up request. We should document the steps to add this client with UPM to the README and the client guide page on the docs.

[thegoldenmule]

@lugehorsam This is awesome!

[lugehorsam]

@novabyte There are a few different ways of doing it which is why I kept it vague. But perhaps I document the asset store and git url examples since I'd imagine those are the two most common ways of doing it.

[lugehorsam]

@novabyte Done. One of the new methods is to download a .tar from the releases page and import it into UPM. However, that will be an unsupported README.md instruction until we make a new release. Thoughts on making a new release?

Edit: Also, the other method (update manifest.json) is unsupported until we make a new release.

[novabyte]

@lugehorsam We should cut a new release but I want to bring in the changes to the .NET client that @thegoldenmule contributed that resolves an issue with encoding JSON numeric primitives.

[lugehorsam]

Added 9498008 because Unity complains if you import a package that doesn't have .meta files.

[novabyte]

@lugehorsam I think we can merge this into master. The latest .NET client release is out and we can prepare for a release of the Unity client.