How can we use curl to download several files concurrently? Even if we need to spawn multiple curl processes, how can I do it from command line or shell function? For example:

```
$ multiCurl <download 1> <download 2> <download 3>

multiCurl () {
  curl <download 1>
  curl <download 2>
  curl <download 3>
}

```

or

```
for link in $(cat download.list); do
  curl <link 1>
  curl <link 2>
  curl <link 3>
  curl <link 4>
done

```