Window: make all windows public

resolves #44

Author: swharden

src/FftSharp/Windows/Cosine.cs

@@ -2,7 +2,7 @@
 
 namespace FftSharp.Windows
 {
-    internal class Cosine : Window, IWindow
+    public class Cosine : Window, IWindow
     {
         public override string Name => "Cosine";
         public override string Description =>

src/FftSharp/Windows/Hamming.cs

@@ -2,7 +2,7 @@
 
 namespace FftSharp.Windows
 {
-    internal class Hamming : Window, IWindow
+    public class Hamming : Window, IWindow
     {
         public override string Name => "Hamming";
         public override string Description =>

src/FftSharp/Windows/Tukey.cs

@@ -4,7 +4,7 @@
 
 namespace FftSharp.Windows
 {
-    internal class Tukey : Window, IWindow
+    public class Tukey : Window, IWindow
     {
         private readonly double Alpha;
 

src/FftSharp/Windows/Welch.cs

@@ -4,7 +4,7 @@
 
 namespace FftSharp.Windows
 {
-    internal class Welch : Window, IWindow
+    public class Welch : Window, IWindow
     {
         public override string Name => "Welch";
         public override string Description =>