Add a lot of documentation

password_message.go

@@ -11,8 +11,11 @@ type PasswordMessage struct {
 	Password string
 }
 
+// Frontend identifies this message as sendable by a PostgreSQL frontend.
 func (*PasswordMessage) Frontend() {}
 
+// Decode decodes src into dst. src must contain the complete message with the exception of the initial 1 byte message
+// type identifier and 4 byte message length.
 func (dst *PasswordMessage) Decode(src []byte) error {
 	buf := bytes.NewBuffer(src)
 
@@ -25,6 +28,7 @@ func (dst *PasswordMessage) Decode(src []byte) error {
 	return nil
 }
 
+// Encode encodes src into dst. dst will include the 1 byte message type identifier and the 4 byte message length.
 func (src *PasswordMessage) Encode(dst []byte) []byte {
 	dst = append(dst, 'p')
 	dst = pgio.AppendInt32(dst, int32(4+len(src.Password)+1))
@@ -35,6 +39,7 @@ func (src *PasswordMessage) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Marshaler.
 func (src *PasswordMessage) MarshalJSON() ([]byte, error) {
 	return json.Marshal(struct {
 		Type     string