* Replaced homegrown Vector2 class with the accelerated one from
System.Numerics.
* Added new Sprite initializers to take advantage of the new
ZOrder field. Changed Point data types to Vector2 where
appropriate.
* Began working on a Sprites sample project.
* .NET Framework sample projects have been removed, as they were
causing issues in Linux.
* .NET Framework samples replaced with .NET Core equivalents.
* Projects now target either .NET Standard 2.0 or .NET Core 2.0.
* Library name was trimmed down to appease .NET Core's native
library loader.
* Library and new sample projects were successfully tested in
Gentoo Linux under .NET Core 2.0.