[Feature Request] Split/Merge a document into pieces based on number of lines/characters

[Thunder T]

Add a feature to Split a document into several equal parts based on certain number of lines/characters, and (optionally) merge them back to a single file.
For example a document containing 3500 lines, is set to split into 1000-line sections, it should split into four sections, the resulting files can be opened in separate tabs.