OCaml: incorrect indentation of multi-line lists

[jonsterling]

In Topiary 0.6.0, the following formatting was accepted:

HTML.section
  [
    class_;
    data_taxon;
  ]

In Topiary 0.6.1, this has regressed to the following weirdly aligned notation:

HTML.section
  [class_;
  data_taxon;
  ]

There are two reasons why the new behaviour is undesirable:

1. Either there should be a newline separating both square brackets from the content, or neither.
2. The second item if the list is aligned with the bracket and not with the first item.