Merge pull request #3 from hailocab/upstream-merge

Upstream merge
Add Session wrapper

With this patch we can now use gocqlx like:

```
session.Query(`SELECT * FROM struct_table`, nil).Get(&v)
```

instead of (old format):

```
gocqlx.Query(session.Query(`SELECT * FROM struct_table`), nil).Get(&v)
```

Signed-off-by: Michał Matczuk <michal@scylladb.com>

migrate/callback.go

@@ -7,7 +7,7 @@ package migrate
 import (
 	"context"
 
-	"github.com/gocql/gocql"
+	"github.com/scylladb/gocqlx"
 )
 
 // CallbackEvent specifies type of the event when calling CallbackFunc.
@@ -21,7 +21,7 @@ const (
 
 // CallbackFunc enables interrupting the migration process and executing code
 // while migrating. If error is returned the migration is aborted.
-type CallbackFunc func(ctx context.Context, session *gocql.Session, ev CallbackEvent, name string) error
+type CallbackFunc func(ctx context.Context, session gocqlx.Session, ev CallbackEvent, name string) error
 
 // Callback is called before and after each migration.
 // See CallbackFunc for details.