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/res_stack.py

@@ -0,0 +1,39 @@
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+import numpy as np
+
+class ResStack(nn.Module):
+    def __init__(self, channel):
+        super(ResStack, self).__init__()
+
+        block_list = [
+            nn.Sequential(
+                nn.LeakyReLU(0.2),
+                nn.ReflectionPad1d(3**i),
+                nn.utils.weight_norm(nn.Conv1d(channel, channel, kernel_size=3, dilation=3**i)),
+                nn.LeakyReLU(0.2),
+                nn.utils.weight_norm(nn.Conv1d(channel, channel, kernel_size=1)),
+            )
+            for i in range(3)
+        ]
+
+        self.block0 = block_list[0]
+        self.block1 = block_list[1]
+        self.block2 = block_list[2]
+
+        shortcut_list = [
+            nn.utils.weight_norm(nn.Conv1d(channel, channel, kernel_size=1))
+            for i in range(3)
+        ]
+
+        self.shortcut0 = shortcut_list[0]
+        self.shortcut1 = shortcut_list[1]
+        self.shortcut2 = shortcut_list[2]
+
+    def forward(self, x):
+        x = self.shortcut0(x) + self.block0(x)
+        x = self.shortcut1(x) + self.block1(x)
+        x = self.shortcut2(x) + self.block2(x)
+        return x
+