Fix some cli options not being passed

[foxblock]

Options edge_path, edge_driver_path and user_agent were never passed to scrape_posts function.
I tried to reduce the amount of duplicate code and move setting of all defaults to parse_args function to reduce sources for this error in the future.

[timf34]

Thanks for catching this @foxblock — you were right that edge_path, edge_driver_path, and user_agent weren't being passed through, and the main() simplification is a good idea.

Since this PR was opened, I've done a larger refactor of the driver/browser management (commit 7fda324) that includes a BrowserManager class with Chrome+Edge support, and the main() function now correctly passes all options through. So the issues this PR addressed have been fixed.

I'll close this in about a week unless there's anything else you'd like to discuss. Thanks again for the contribution — and for the great work on the CSS selectors fix in PR #41 which was just merged!