Additional support for command-based robots (#116)

* Add a CommandRobot base

Takes care of the boilerplate for running the scheduler.
Does not implement any of the logic for selecting or creating autonomous modes.

* Add SubsystemCommand to extras

It behaves as a regular command, but automatically calls `.Requires` on the provided subsystem and stores a reference to it as `m_subsystem`

* Fix comments to provide more accurate description

WPILib.Extras/CommandRobot.cs

@@ -0,0 +1,26 @@
+using WPILib.Commands;
+
+namespace WPILib.Extras
+{
+    /// <summary>
+    /// Implements the boilerplate needed to use an <see cref="IterativeRobot"/>
+    /// with the command-based model, by running the scheduler as needed.
+    /// </summary>
+    public abstract class CommandRobot : IterativeRobot
+    {
+        // This function is called periodically while disabled
+        public override void DisabledPeriodic() => Scheduler.Instance.Run();
+
+        // This function is called periodically during autonomous
+        public override void AutonomousPeriodic() => Scheduler.Instance.Run();
+
+        // This function is called when the disabled button is hit.
+        public override void DisabledInit() { }
+
+        // This function is called periodically during operator control
+        public override void TeleopPeriodic() => Scheduler.Instance.Run();
+
+        // This function is called periodically during test mode
+        public override void TestPeriodic() => LiveWindow.LiveWindow.Run();
+    }
+}

WPILib.Extras/SubsystemCommand.cs

@@ -0,0 +1,37 @@
+using System;
+using WPILib.Commands;
+
+namespace WPILib.Extras
+{
+    /// <summary>
+    /// A <see cref="SubsystemCommand"/> depends on the given <see cref="Subsystem"/>.
+    /// It stores a local reference to its <see cref="Subsystem" /> to ease access.
+    /// </summary>
+    public abstract class SubsystemCommand : Command
+    {
+        protected readonly Subsystem m_subsystem;
+
+        /// <summary>
+        /// Creates a new <see cref="SubsystemCommand"/> which will depend on the given <see cref="Subsystem"/>.
+        /// </summary>
+        /// <param name="action">The <see cref="Action"/> to run.</param>
+        public SubsystemCommand(Subsystem subsystem)
+        {
+            Requires(subsystem);
+            m_subsystem = subsystem;
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="SubsystemCommand"/> with a specific name, 
+        /// which will depend on the given <see cref="Subsystem"/>.
+        /// </summary>
+        /// <param name="subsystem">The <see cref="Subsystem"/> to require.</param>
+        /// <param name="name">The name for the command.</param>
+        public SubsystemCommand(Subsystem subsystem, string name)
+            : base(name)
+        {
+            Requires(subsystem);
+            m_subsystem = subsystem;
+        }
+    }
+}

WPILib.Extras/WPILib.Extras.csproj

@@ -80,6 +80,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="SubsystemCommand.cs" />
     <Compile Include="ActionCommand.cs" />
     <Compile Include="AttributedCommandModel\AttributedRobot.cs" />
     <Compile Include="AttributedCommandModel\ButtonMethod.cs" />
@@ -89,6 +90,7 @@
     <Compile Include="AttributedCommandModel\RunCommandAttribute.cs" />
     <Compile Include="AttributedCommandModel\RunCommandOnJoystickAttribute.cs" />
     <Compile Include="AttributedCommandModel\RunCommandOnNetworkKeyAttribute.cs" />
+    <Compile Include="CommandRobot.cs" />
     <Compile Include="LabVIEWRobot.cs" />
     <Compile Include="NavX\AHRS.cs" />
     <Compile Include="NavX\ContinuousAngleTracker.cs" />