Add missing doc

meta.go

@@ -207,6 +207,7 @@ func (s *Stmt) ColumnTypeAffinity(index int) Affinity {
 	return affinity
 }
 
+// Affinity returns the type affinity of the column.
 func (c Column) Affinity() Affinity {
 	return typeAffinity(c.DataType)
 }

pool.go

@@ -21,6 +21,7 @@ type Pool struct {
 	idleTimeout time.Duration
 }
 
+// ConnOpen is the signature of connection factory.
 type ConnOpen func() (*Conn, error)
 
 // NewPool creates a connection pool.
@@ -140,6 +141,7 @@ func (p *Pool) Close() {
 	p.factory = nil
 }
 
+// IsClosed returns true when the pool has been closed.
 func (p *Pool) IsClosed() bool {
 	return p.factory == nil
 }