Introduce Exec interface and implementers (#1)

Reviewed-on: #1

schema/schema.go

@@ -0,0 +1,11 @@
+package schema
+
+// Interface that descibes a DB schema descripotor part.
+// eg.: Table, Column, Constraints etc.
+type SchemaDescriptor interface {
+	getDDL() (string, error)
+	GetSelectDML() (string, error)
+	GetInsertDML(count int) (string, error)
+	GetUpdateDML() (string, error)
+	GetDeleteDML(count int) (string, error)
+}