Add more guidance on scope for constants

[tyler-french]

Hoping to get some opinions on this.

One pattern I see a lot is with making global constants for values that are only used within a certain function.

For example

const _defaultPort = 8000

func something() {
  doSomething(_defaultPort)
  port := _defaultPort
}

In my opinion, there should be an adjustment to the # Reduce Scope of Variables section to include more emphasis on what to do with Constants.

I mostly want to get opinions here, but I generally would prefer to change the above code to the following:

func something() {
  const defaultPort = 8000
  doSomething(defaultPort)
  port := defaultPort
}

Thoughts?

[tyler-french]

Maybe a follow-up, what about things like types and enums:

func doSomething(input string) {
	type x string
	const (
		y x = "0"
		z x = "1"
	)
	...

[sywhang]

https://github.com/uber-go/guide/blob/master/style.md#reduce-scope-of-variables kind of covers this, IMO. Perhaps adding some more examples with types/consts can be helpful?