Strong name, remove dependencies, integrate with Spreads

[buybackoff]

Upstream is dead, while the library - in general - is just a P/Invoke wrapper, similar to SQLite, Blosc, etc. As I am always against binary dependencies for stable and permissive code, I should just add Spreads extensions right here and go with a fork.

• Need to integrate dependencies as source (DynamicInterop is MIT, R.NET itself is BSD).
• Add strong name with a public key (this alone requires a fork recently)
• Add R cursors and extension methods that work together with the R package and call by name functions saved in an environment on disk.

Should re-think how to implement online incremental algos in R. Obviously, we need to store state inside R and have a function that updates it with new values and returns the updated state, but the devil is in implementation detail.