zhangi

feat: add WithKeepSeparator option for RecursiveCharacter

1

Fix issue #720 Reference Implementation In Python: [RecursiveCharacterTextSplitter](https://api.python.langchain.com/en/latest/_modules/langchain_text_splitters/character.html#RecursiveCharacterTextSplitter)

## Proposal add support of `keep_separator` textsplitter.NewRecursiveCharacter, which is enabled by default in Python implementation. Refer to [RecursiveCharacterTextSplitter](https://api.python.langchain.com/en/latest/character/langchain_text_splitters.character.RecursiveCharacterTextSplitter.html#langchain_text_splitters.character.RecursiveCharacterTextSplitter) ## Issue without `keep_separator`, the current implementation produces chunks whose length are...