Create mmlu.yaml

Begin MMLU implementation

lm_eval/tasks/mmlu/mmlu.yaml

+group:
+  - multiple_choice
+task: mmlu
+dataset_path: cais/mmlu
+dataset_name: null
+output_type: multiple_choice
+training_split: train
+validation_split: validation
+test_split: test
+template_aliases: "{% set answer_choices = [distractor1, distractor2, distractor3, correct_answer] %}{% set gold = 3 %}" # set the list of possible answer choices, and set what this doc's gold label idx is
+doc_to_text: "{{support.lstrip()}}\nQuestion: {{question}}\nAnswer:"
+doc_to_target: " {{correct_answer}}"
+gold_alias: "{{gold}}" # this will be cast to an int.
+metric_list:
+  - metric: acc
+    aggregation: mean
+    higher_is_better: true
+  - metric: acc_norm
+    aggregation: mean
+    higher_is_better: true
+  - metric: acc_mutual_info
+    aggregation: mean
+    higher_is_better: true