encapsulate fft chain in its own class

csdr/chain/__init__.py

@@ -0,0 +1,16 @@
+class Chain(object):
+    def __init__(self, *workers):
+        self.workers = workers
+        stage = None
+        for w in self.workers:
+            if stage is not None:
+                w.setInput(stage.getBuffer())
+            stage = w
+        self.buffer = stage.getBuffer()
+
+    def stop(self):
+        for w in self.workers:
+            w.stop()
+
+    def getBuffer(self):
+        return self.buffer