Removes code duplication (code climate)

No gain but it's "better": https://codeclimate.com/github/Mogztter/asciidoctor/compare/code-climate
Scala Option would be great, something like http://blog.sharetribe.com/2014/06/02/option-pattern-maybe-monad-in-ruby/

```ruby
spec.add(get_halign(colspec))
spec.add(get_valign(rowspec))
# Removes None
spec.flatten
```