distinguish between idle and released on buttons

src/Input/ButtonState.cs

@@ -8,6 +8,8 @@
 		public bool IsHeld => ButtonStatus == ButtonStatus.Held;
 		public bool IsDown => ButtonStatus == ButtonStatus.Pressed || ButtonStatus == ButtonStatus.Held;
 		public bool IsReleased => ButtonStatus == ButtonStatus.Released;
+		public bool IsIdle => ButtonStatus == ButtonStatus.Idle;
+		public bool IsUp => ButtonStatus == ButtonStatus.Idle || ButtonStatus == ButtonStatus.Released;
 
 		public ButtonState(ButtonStatus buttonStatus)
 		{
@@ -18,26 +20,34 @@
 		{
 			if (isPressed)
 			{
-				if (ButtonStatus == ButtonStatus.Pressed)
-				{
-					return new ButtonState(ButtonStatus.Held);
-				}
-				else if (ButtonStatus == ButtonStatus.Released)
+				if (IsUp)
 				{
 					return new ButtonState(ButtonStatus.Pressed);
 				}
-				else if (ButtonStatus == ButtonStatus.Held)
+				else
 				{
 					return new ButtonState(ButtonStatus.Held);
 				}
 			}
-
+			else
+			{
+				if (IsDown)
+				{
 					return new ButtonState(ButtonStatus.Released);
 				}
+				else
+				{
+					return new ButtonState(ButtonStatus.Idle);
+				}
+			}
+		}
 
+		/// <summary>
+		/// Combines two button states. Useful for alt controls or input buffering.
+		/// </summary>
 		public static ButtonState operator |(ButtonState a, ButtonState b)
 		{
-			if (a.ButtonStatus == ButtonStatus.Released)
+			if (a.ButtonStatus == ButtonStatus.Idle || a.ButtonStatus == ButtonStatus.Released)
 			{
 				return b;
 			}

src/Input/ButtonStatus.cs

@@ -3,15 +3,19 @@
 	public enum ButtonStatus
 	{
 		/// <summary>
-		/// Indicates that the input is not pressed.
+		/// Indicates that the button was not pressed last frame and is still not pressed.
+		/// </summary>
+		Idle,
+		/// <summary>
+		/// Indicates that the button was released this frame.
 		/// </summary>
 		Released,
 		/// <summary>
-		/// Indicates that the input was pressed this frame.
+		/// Indicates that the button was pressed this frame.
 		/// </summary>
 		Pressed,
 		/// <summary>
-		/// Indicates that the input has been held for multiple frames.
+		/// Indicates that the button has been held for multiple frames.
 		/// </summary>
 		Held
 	}

src/Input/Keyboard.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Runtime.InteropServices;
 using SDL2;
 
 namespace MoonWorks.Input