feature request: "skip-tables", "structure-tables", more options for db backups

[aaronbauman]

drush offers many options which are not available to "terminus site backup" command.

Since commands like skip-tables and structure-tables are not supported, synching the pantheon-hosted database with non-pantheon environment (e.g. local) is exceedingly tedious.

if offering equivalent functionality is not possible, what about providing a pantheon-specific drush command to extend compatibility for sql-dump and/or sql-sync?

[bensheldon]

@aaronbauman There is some momentum coalescing around tools for syncing and piping databases in #235. I think your suggestions would contribute well to that discussion.