Create the first release #131

FlagEmbedding

• Update Embedding Models bge-*-v1.5:
  • alleviate the issue of the similarity distribution
  • the new models can do retrieval tasks without instruction, but still recommend using instruction which can have a better performance.
• New Models bge-reranker-*: cross-encoders that can rerank the top-k retrieved results
• Specify using normalization in the configuration for sentence-transformers, thanks to skirres.
  Now users have no need to set normalize_embeddings=True manually when using sentence-transformers.

C-MTEB

• Add two cross-lingual retrieval tasks: T2RerankingZh2En and T2RerankingEn2Zh.