Remove unspecified gender in favor of Option.

src/backends/av_foundation.rs

@@ -298,9 +298,9 @@ impl Backend for AvFoundation {
                 let name: CFString = unsafe { msg_send![*v as *const Object, name] };
                 let gender: i64 = unsafe { msg_send![*v as *const Object, gender] };
                 let gender = match gender {
-                    0 => Gender::Male,
-                    1 => Gender::Female,
-                    _ => Gender::Unspecified,
+                    0 => Some(Gender::Male),
+                    1 => Some(Gender::Female),
+                    _ => None,
                 };
                 let language: CFString = unsafe { msg_send![*v as *const Object, language] };
                 let language = language.to_string();

src/lib.rs

@@ -704,7 +704,6 @@ impl Drop for Tts {
 
 #[derive(Clone, Copy, Debug)]
 pub enum Gender {
-    Unspecified,
     Male,
     Female,
 }
@@ -713,7 +712,7 @@ pub enum Gender {
 pub struct Voice {
     pub(crate) id: String,
     pub(crate) name: String,
-    pub(crate) gender: Gender,
+    pub(crate) gender: Option<Gender>,
     pub(crate) language: LanguageIdentifier,
 }
 
@@ -726,7 +725,7 @@ impl Voice {
         self.name.clone()
     }
 
-    pub fn gender(&self) -> Gender {
+    pub fn gender(&self) -> Option<Gender> {
         self.gender
     }