Rewrite the varnish cookbook article

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #1505, #4176
additionally, the only thing that is different between 2 and 3 in this file is the line about esi. and i guess a varnish2 user will easily find that when googling. so i propose to remove it.

can somebody who merges doc PRs confirm whether its ok to remove varnish2 examples?