Added beginning of function to preserve settings

This is the beginning of a solution to issue #3. Right now, it is only
able to preserve keys. In a later commit, modifiers, mouse settings,
etc. will be added as well.

src/main.rs

@@ -208,6 +208,16 @@ fn main() {
                 {
                     check_length(&pedal, &input);
 
+                    let mut unused_pedals: Vec<u8> = Vec::new();
+
+                    for number in 0..3 {
+                        if !pedal.contains(&(number as u8)) {
+                            unused_pedals.push(number);
+                        }
+                    }
+
+                    pedals.refresh_values(unused_pedals);
+
                     for (i, pedal) in pedal.iter().enumerate() { 
                         pedals.set_key(*pedal as usize, input[i].as_str()); 
                     }

src/pedal_operations.rs

@@ -378,4 +378,25 @@ impl Pedals {
     
         goodbye();
     }
+    
+    /// Prevent the application from purging pedals that are not
+    /// explicitly set
+    pub fn refresh_values(& mut self, peds: Vec<u8>) {
+        
+        // First read from pedals that are defined in peds
+        for (i, ped) in peds.iter().enumerate() {
+            // Read value from pedal and directly translate it to a key
+            let mut key_value = self.read_pedal(ped);
+
+            match Type::u8_to_enum(key_value[1]) {
+                Some(Type::Key) => {
+                    self.set_type(*ped as usize, Type::Key);
+                    self.ped_data[*ped as usize].data[3] = key_value[3];
+                },
+
+                None => error!("The key type which was returned by the pedal was invalid!"),
+                _ => {} 
+            };
+        }
+    }
 }