[wpimath] Use jinja for codegen (#3574)

While not really needed for wpimath, it will make more complex codegen
in the future significantly easier.

wpimath/src/generate/GenericNumber.java.jinja

@@ -0,0 +1,31 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.math.numbers;
+
+import edu.wpi.first.math.Nat;
+import edu.wpi.first.math.Num;
+
+/**
+ * A class representing the number {{ num }}.
+*/
+public final class N{{ num }} extends Num implements Nat<N{{ num }}> {
+  private N{{ num }}() {
+  }
+
+  /**
+   * The integer this class represents.
+   *
+   * @return The literal number {{ num }}.
+  */
+  @Override
+  public int getNum() {
+    return {{ num }};
+  }
+
+  /**
+   * The singleton instance of this class.
+  */
+  public static final N{{ num }} instance = new N{{ num }}();
+}