Improve pipeline indentation

Following @josevalim suggestion(https://github.com/elixir-lang/vim-elixir/pull/54#issuecomment-31294774)
for pipeline indentation.

Using:

```elixir
bar
|> baz
|> quux

foo = bar
      |> baz
      |> quux
```
partially fixed case indentation

- insertion mode still doesn't work correctly
Merge pull request #61 from kassio/master

Improve pipeline indentation