Point: add some documentation comments (NFC)

Add some missing documentation comments and section markers for `Point`.

Author: compnerd

Sources/SwiftWin32/CG/Point.swift

@@ -1,25 +1,46 @@
 // Copyright © 2019 Saleem Abdulrasool <[email protected]>
 // SPDX-License-Identifier: BSD-3-Clause
 
+/// A structure that contains a point in a two-dimensional coordinate system.
 public struct Point {
-  public static let zero: Point = Point(x: 0, y: 0)
-
-  public var x: Double
-  public var y: Double
-
-  public init(x: Float, y: Float) {
-    self.init(x: Double(x), y: Double(y))
-  }
+  // MARK - Creating Point Values
 
+  /// Creates a point with coordinates specified as floating-point values.
   public init(x: Double, y: Double) {
     self.x = x
     self.y = y
   }
 
+  /// Creates a point with coordinates specified as integer values.
   public init(x: Int, y: Int) {
     self.init(x: Double(x), y: Double(y))
   }
 
+  // MARK - Special Values
+
+  /// The point with location (0,0).
+  public static var zero: Point {
+    Point(x: 0, y: 0)
+  }
+
+  /// Creates a point with location (0,0).
+  public init() {
+    self.x = 0.0
+    self.y = 0.0
+  }
+
+  // MARK - Geometric Properties
+
+  /// The x-coordinate of the point.
+  public var x: Double
+
+  /// The y-coordinate of the point.
+  public var y: Double
+
+  // MARK - Transforming Points
+
+  /// Returns the point resulting from an affine transformation of an existing
+  /// point.
   public func applying(_ transform: AffineTransform) -> Point {
     return Point(x: transform.a * self.x + transform.c * self.y + transform.tx,
                  y: transform.b * self.x + transform.d * self.y + transform.ty)