Add Cofree

We probably want to keep some version bounds, otherwise some conflicts can arise. Can we make it:

```
"purescript-control": "~0.2.1",
"purescript-either": "~0.1.3",
"purescript-exists": "*",
"purescript-transformers": "~0.2.0",
"purescript-lazy": "~0.1.0",
"purescript-foldable-traversable": "~0.1.3"
```