v0.8.0

Changelog:

• Relicensed under MIT license
• Add RoBERTa
• Add wav2vec
• Add WMT'19 models
• Add initial ASR code
• Changed torch.hub interface (generate renamed to translate)
• Add --tokenizer and --bpe
• f812e52: Renamed data.transforms -> data.encoders
• 654affc: New Dataset API (optional)
• 47fd985: Deprecate old Masked LM components
• 5f78106: Set mmap as default dataset format and infer format automatically
• Misc fixes for sampling
• Misc fixes to support PyTorch 1.2