database/sql: use complete sentences in new docs

Change-Id: Icb842a80cab2b07b9ace1e8e14c4a19c48a92c43
Reviewed-on: https://go-review.googlesource.com/34247
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>

src/database/sql/sql.go

@@ -72,19 +72,26 @@ func Drivers() []string {
 	return list
 }
 
-// A NamedArg used as an argument to Query or Exec
-// binds to the corresponding named parameter in the SQL statement.
+// A NamedArg is a named argument. NamedArg values may be used as
+// arguments to Query or Exec and bind to the corresponding named
+// parameter in the SQL statement.
+//
+// For a more concise way to create NamedArg values, see
+// the Named function.
 type NamedArg struct {
 	_Named_Fields_Required struct{}
 
-	// Name of the parameter placeholder. If empty the ordinal position in the
-	// argument list will be used.
+	// Name is the name of the parameter placeholder.
+	//
+	// If empty, the ordinal position in the argument list will be
+	// used.
 	//
 	// Name must omit any symbol prefix.
 	Name string
 
-	// Value of the parameter. It may be assigned the same value types as
-	// the query arguments.
+	// Value is the value of the parameter.
+	// It may be assigned the same value types as the query
+	// arguments.
 	Value interface{}
 }