[Question] How to send headers with custom response?
i'm trying to test SSE (Server Sent Events), but i'm having trouble with Prologue's ctx, headers and response. I don't know if there's  a bug, or maybe an FR for an improvement to the docs, or maybe an SSE example.

Example 1
```
#sends response with code and data, but not custom headers. 
  ctx.handled = true  
  ctx.response.setHeader("Content-Type", "text/event-stream")
  ctx.response.setHeader("Cache-Control", "no-cache")  
  let data = "data: some cool data, man!"
  await ctx.respond(Http200, data)

```
Example 2
  ```
#sends custom headers, but not data
  ctx.handled = true  
  ctx.response.setHeader("Content-Type", "text/event-stream")
  ctx.response.setHeader("Cache-Control", "no-cache")
  let data = "data: some cool data, man!"
  #just trying to force it to send my headers, which works, but doesn't include my data...
  await ctx.respond()
```
I thought using setHeader() would add the headers to the ctx for me, and it does b/c i can echo after setting, but they don't get sent with the response when calling ctx.respond in example 1. 

How to send the headers with the response (with my data) to override the default "text/plain" header type so SSE will work?

thanks