set up for better async handling

src/wavetable.rs

@@ -1,7 +1,8 @@
 pub trait Wavetable {
     type OutputType: Default + Copy;
     /// get next sample
-    fn next(&mut self) -> Self::OutputType;
+    fn next(&mut self);
+    fn get_value(&self) -> Self::OutputType;
     fn size(&self) -> usize;
 }
 
@@ -16,13 +17,15 @@ pub struct SimpleWavetable<'a, T: Copy> {
 
 impl<'a, T: Copy + Default> Wavetable for SimpleWavetable<'a, T> {
     type OutputType = T;
-    fn next(&mut self) -> Self::OutputType {
-        let value = self.table[self.index];
+    fn next(&mut self) {
         self.index += 1;
         if self.index > self.table.len() - 1 {
             self.index = 0;
         }
-        value
+    }
+
+    fn get_value(&self) -> Self::OutputType {
+        self.table[self.index]
     }
 
     fn size(&self) -> usize {