Added events as an optional export parameter

This PR modifies the export process. Before: Export the global `instrument.get_events()` After: If the user has provided an explicit list of events, export those. Otherwise, export the global `instrument.get_events()` Sometimes I want to export a subset of the overall events. So I make a copy using `vim.fn.copy(instrument.get_events())`, get a slice of those events, and now just need a way to export that slice. This PR makes that possible.