feat: Replace hasher trait with hasher crate. #44

rewrite: Use rc and refcell to avoid all clones. #43

refactor: Add batch for db #38

• Feat: impl get_proof and verify_proof #33
• Refactor: change db in trie from mut ref to Arc #35

Fix: Avoid delete stale root. #30
Refactor: Add light mode for mem DB. #31

refactor: Implement debug internally to avoid the hassle of external users. #29

Feat: DB trait can be thread-safely copied #27

• Refactor: avoid unnecessarily clone in insert function #18
• Fix: delete all stale keys #19