Release v2.3.0

[roseduan]

🚀 New Features

• use BTree as the default memory data structure.
  • the old Radix will be removed, and the iterator too.

🎄 Enhancements

🎠 Community

• Thanks to @Jeremy-Run
  • remove merge file after tests (remove merge file #250)
  • replace original file and rebuilt index after merge (replace original file and rebuilt index after merge #255)
• Thanks to @SYaoJun
  • fix: single quote error in README (fix: single quote error in README #256)
• Thanks to @weijiew
  • add btree Ascend、Descend method and unitest. (add btree Ascend、Descend method and unitest. #257)

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This discussion was created from the release Release v2.3.0.