migrations statuses func

[w1kend]

Hi!
Someone asked in #255 about having function for getting migration statuses.

So if you want to have this func we can discuss it, because I have some thoughts additionally to the changes.

1. looks like the Migrations type should have this function

func (ms Migrations) Records() ([]MigrationRecord, error) {}

2. add a tstamp to query in dbVersionQuery(db *sql.DB) in case that someone needs it.

[mfridman]

Thanks for the PR, unfortunately we didn't end up merging it. I'm going to close this in favor of

func (p *Provider) HasPending(context.Context) (bool, error) {}

added in #751