Add basic documentation.

src/lib.rs

@@ -1,3 +1,8 @@
+/*!
+ * a Text-To-Speech (TTS) library providing high-level interfaces to a variety of backends.
+ * Currently supported backends are [Speech Dispatcher](https://freebsoft.org/speechd) (Linux).
+*/
+
 use std::boxed::Box;
 
 mod backends;
@@ -21,6 +26,10 @@ trait Backend {
 pub struct TTS(Box<Backend>);
 
 impl TTS {
+
+    /**
+     * Create a new `TTS` instance with the specified backend.
+    */
     pub fn new(backend: Backends) -> TTS {
         match backend {
             #[cfg(target_os = "linux")]
@@ -28,38 +37,62 @@ impl TTS {
         }
     }
 
+    /**
+     * Speaks the specified text, optionally interrupting current speech.
+    */
     pub fn speak<S: Into<String>>(&self, text: S, interrupt: bool) -> &Self {
         self.0.speak(text.into().as_str(), interrupt);
         self
     }
 
+    /**
+     * Stops current speech.
+    */
     pub fn stop(&self) -> &Self {
         self.0.stop();
         self
     }
 
+    /**
+     * Gets the current speech rate.
+    */
     pub fn get_rate(&self) -> u8 {
         self.0.get_rate()
     }
 
+    /**
+     * Sets the desired speech rate.
+    */
     pub fn set_rate(&self, rate: u8) -> &Self {
         self.0.set_rate(rate);
         self
     }
 
+    /**
+     * Gets the current speech pitch.
+    */
     pub fn get_pitch(&self) -> u8 {
         self.0.get_pitch()
     }
 
+    /**
+     * Sets the desired speech pitch.
+    */
     pub fn set_pitch(&self, pitch: u8) -> &Self {
         self.0.set_pitch(pitch);
         self
     }
 
+    /**
+     * Gets the current speech volume.
+    */
     pub fn get_volume(&self) -> u8 {
         self.0.get_volume()
     }
 
+    /**
+     * Sets the desired speech volume.
+    */
     pub fn set_volume(&self, volume: u8) -> &Self {
         self.0.set_volume(volume);
         self