Add MPD client implementation

internal/client/errors.go

@@ -0,0 +1,19 @@
+package client
+
+import "fmt"
+
+type ValueParseErr struct {
+	field string
+	value string
+}
+
+func newValueParseError(field string, value string) ValueParseErr {
+	return ValueParseErr{
+		field: field,
+		value: value,
+	}
+}
+
+func (e ValueParseErr) Error() string {
+	return fmt.Sprintf("failed to parse %s value: %s", e.field, e.value)
+}