rewrite quite many trie codes, _update_kv_node not finished yet
finished: _update_kv_node. need testing
fix some bugs, still not complete
Revert package-wide logging config from #35
1. close #34: rewritten update/get code
2. need to check correctness using data from the `test` project
remove inadvertently re-commited the code expected to be removed
close #45
close #44
close #40
close #40: down key limitation to 32 bytes
add a fail scenario
add tips for debug in readme