Refactor project files, add BRCPath variable for assemblies and use audio streaming instead of data caching

[LunaCapra]

This PR does the following:

• Make the .csproj much more readable and usable, which in turn also makes the entire project more easily loadable when forking or cloning it.
• Add usage of the BRCPath environment variable in order for the game assembly to not have to be included or hardcoded to point to the game's directory. This is inspired by Slop Crew's method of doing it and is much more versatile and less prone to errors.
• Enable Audio Streaming as a feature instead of caching the audio data. This is a very common technique for background music, as it reduces load times drastically in turn for a little more CPU usage. This is implemented using Unity's DownloadHandlerAudioClip.streamAudio property in the UnityWebRequest already used to load files.