Add a lot of documentation

startup_message.go

@@ -19,8 +19,11 @@ type StartupMessage struct {
 	Parameters      map[string]string
 }
 
+// Frontend identifies this message as sendable by a PostgreSQL frontend.
 func (*StartupMessage) 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 *StartupMessage) Decode(src []byte) error {
 	if len(src) < 4 {
 		return errors.Errorf("startup message too short")
@@ -66,6 +69,7 @@ func (dst *StartupMessage) 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 *StartupMessage) Encode(dst []byte) []byte {
 	sp := len(dst)
 	dst = pgio.AppendInt32(dst, -1)
@@ -84,6 +88,7 @@ func (src *StartupMessage) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Marshaler.
 func (src *StartupMessage) MarshalJSON() ([]byte, error) {
 	return json.Marshal(struct {
 		Type            string