first commit; melgan support (perhaps bloated)

I copied this from my old and messy `tacotron-melgan` repo, where I had
previously experimented with running the two models in a pipeline.

I'll be moving over all the JIT pieces here and cleaning up when I can.

melgan-swpark/model_melgan/identity.py

@@ -0,0 +1,12 @@
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+
+
+class Identity(nn.Module):
+    def __init__(self):
+        super(Identity, self).__init__()
+
+    def forward(self, x):
+        return x
+