PyMilvus v2.0.0rc4 Release

Release date：2021-08-16
Compatible with Milvus v2.x

Fixed bugs:

• Remove a mistake check in search future (#608)
• Fix the parameter timeout of load_collection API not working problem (#620)
• Fix the logic of retry for RPC calling (#622)

Enhancements:

• Add a check of parameter anns_field in search (#609)
• Add a check of parameter search_data in search (#610)
• Add a check of parameter output_fields in search (#613)
• Set the default metric of calc_distance API (#616)
• Provide more info when create index failed (#618)
• Support output binary vector in query API (#623)