Add helloweb snippet

[thomasdarimont]

helloweb generates small web app with an http endpoint
which returns a greeting and the current time.

This is can be used to quickly generate a minimal web app
for demo purposes.

The generated code looks like:

package main

import (
	"fmt"
	"net/http"
	"time"
)

func greet(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello World! %s", time.Now())
}

func main() {
	http.HandleFunc("/", greet)
	http.ListenAndServe(":8080", nil)
}

[msftclas]

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. We will now review your pull request.
Thanks,
Microsoft Pull Request Bot

[msftclas]

@thomasdarimont, thanks for signing the contribution license agreement. We will now validate the agreement and then the pull request.

Thanks, Microsoft Pull Request Bot

[ramya-rao-a]

This snippet is now out in the latest update to the Go extension 0.6.64