revert on commit 98daafa8b09406b

but multiple styles are collected and output at once
[Dot] fix previous commit
   - style of subgraph doesn't use square bracket
   - style of subgraph use the semicolon separator

   - simplify the code by using the fact that dot understand lists that
    end with the list separator
Merge pull request #11 from bobot/revert-style-list

[Dot] fix previous commit