Drush 10/11 compatibility

I've done the initial conversion to scratch my itch, sorry I may not have any capacity to follow through.

Thanks. Yeah, the UX of the commands isn't great, but it's working as it did before as far as I see, so improving it seems like a separate issue.

Removed drush.inc and fixed some php warnings with the question.

Merged.

Thanks so much!

Automatically closed - issue fixed for 2 weeks with no activity.