add(Scrollable): init function with corresponding usages

src/input.zig

@@ -68,6 +68,8 @@ pub const Key = packed struct {
         return std.meta.eql(this, other);
     }
 
+    // TODO might be useful to use the std.ascii stuff!
+
     /// Determine if the `Key` is an ascii character that can be printed to
     /// the screen. This means that the code point of the `Key` is an ascii
     /// character between 32 - 255 (with the exception of 127 = Delete) and no