Array of tables

The Christmas pull request. Array of tables for the people.
Could also be written as:

```ocaml
let str =
  "[[a.b.c]]\n\
   field1 = 1\n\
   field2 = 2\n\
   [[a.b.c]]\n\
   field1 = 10\n\
   field2 = 20"
```