All indentation was normalized by rubocop auto-correct at 80e66cc4d9.
But comments was still kept absolute position. This commit aligns
comments with method definitions for consistency.
```ruby
ActiveSupport::Duration.parse('P3Y6M4DT12H30M5S')
(3.years + 3.days).iso8601
```
Inspired by Arnau Siches' [ISO8601 gem](https://github.com/arnau/ISO8601/)
and rewritten by Andrey Novikov with suggestions from Andrew White. Test
data from the ISO8601 gem redistributed under MIT license.
(Will be used to support the PostgreSQL interval data type.)