Feature request: starting date for history conversion

[TimurKelman]

Since the incremental migration is out of scope, maybe some way to start the conversion from given point in time (to only export history from last month for example) could be implemented more easily.

[trevorr]

This project is not under active development, at least by me, so feature requests are unlikely to be picked up by anyone else. You're welcome to submit a pull request though. PRs should follow the style of the existing code and either be low-risk or include some sort of testing instructions.