Prune dead code
Remove one as well as the rows vestige

The one API was problematic. You could accidentally send DDL to it and
get -1 for rowcount instead of 0, and then what? Better to scrap it in
favor of one_or_zero, which you're less likely to confuse with run
anyway.
Kill off get_cursor

Turns out we only need get_transaction.
Bump version to 2.0.0rc1