Add roberta implementation on MC-TACO

[PosoSAgapo]

Roberta implementation on MC-TACO dataset, this implementation works with the Roberta script file.
The training and testing procedure is same with Bert, just change the Bert script to Roberta script.
Futures like distributed trainning and fp16 are removed, this implementation is based on Huggingface package, which means it could be simply tested on other language models with just little change in Huggingface's model specification parameter