added config class for gpt2 medium model

Author: marcusklasson

GPT2/config.py

@@ -22,4 +22,29 @@ def __init__(
         self.n_layer = n_layer
         self.n_head = n_head
         self.layer_norm_epsilon = layer_norm_epsilon
-        self.initializer_range = initializer_range
+        self.initializer_range = initializer_range
+        
+class GPT2MediumConfig(object):
+    """ Config for GPT-2 Medium (355M params). 
+    Config file can be downloaded with:
+    curl --output gpt2-medium-config.json https://s3.amazonaws.com/models.huggingface.co/bert/gpt2-medium-config.json
+    """
+    def __init__(
+            self,
+            vocab_size_or_config_json_file=50257,
+            n_positions=1024,
+            n_ctx=1024,
+            n_embd=1024,
+            n_layer=24,
+            n_head=16,
+            layer_norm_epsilon=1e-5,
+            initializer_range=0.02,
+    ):
+        self.vocab_size = vocab_size_or_config_json_file
+        self.n_ctx = n_ctx
+        self.n_positions = n_positions
+        self.n_embd = n_embd
+        self.n_layer = n_layer
+        self.n_head = n_head
+        self.layer_norm_epsilon = layer_norm_epsilon
+        self.initializer_range = initializer_range