Add a lot of documentation

backend_key_data.go

@@ -12,8 +12,11 @@ type BackendKeyData struct {
 	SecretKey uint32
 }
 
+// Backend identifies this message as sendable by the PostgreSQL backend.
 func (*BackendKeyData) Backend() {}
 
+// 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 *BackendKeyData) Decode(src []byte) error {
 	if len(src) != 8 {
 		return &invalidMessageLenErr{messageType: "BackendKeyData", expectedLen: 8, actualLen: len(src)}
@@ -25,6 +28,7 @@ func (dst *BackendKeyData) 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 *BackendKeyData) Encode(dst []byte) []byte {
 	dst = append(dst, 'K')
 	dst = pgio.AppendUint32(dst, 12)
@@ -33,6 +37,7 @@ func (src *BackendKeyData) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Marshaler.
 func (src *BackendKeyData) MarshalJSON() ([]byte, error) {
 	return json.Marshal(struct {
 		Type      string