feature: Simple type-declaration statements

As simplification of `var` declaration，Can you consider adding `type` declarations to the ranks of simplification?

exp:

```go
type ExampleArgs struct {
	X int
}
type ExampleReply struct {
	Y int
}
```
after:

```go
type (
	ExampleArgs struct {
		X int
	}
	ExampleReply struct {
		Y int
	}
)

```