Release 20.1.0

Feature: Update to Steamworks SDK 1.53

Changed: Automatically cleanup old Steam dlls in the root of the project (#479)
Changed: Added a nuspec for all-in-one package (#481) (Thanks to @Akarinnnnn)
Changed: Added STEAMWORKS_NET define (#484) (Thanks to @JamesMcGhee)

Fixed: Remove unused SteamUnifiedMessages.meta causing warnings

Full Changelog: 20.0.0...20.1.0

Unity upgrading notice: Due to the new Unity package format you must completely remove Steamworks.NET if you have a release prior to 20.0.0.

Unity version notice: As of Release 20.0.0 the minimum supported Unity Version is the LTS release "2019.4" due to the package support.

Unity Package Manager url: https://github.com/rlabrecque/Steamworks.NET.git?path=/com.rlabrecque.steamworks.net#20.1.0

Get the .unitypackage if you are using Unity.
The prebuilt "Standalone" package is for non-Unity projects ONLY.