Parser reviewed; some bugs fixed. 

Hey!
This code snippet produces the following changes:
- Refactoring of method `initialize` from `parser.rb` was done;
- Headings and tables within a quote or center block are handled properly. It closes issue bdewey/org-ruby#35;
- No need to accumulate `@buffered_lines`, this variable was removed from `output_buffer.rb`;
- Indentation for code blocks was done. It closes issue bdewey/org-ruby#31;
- Adds paragraphs with `class=title` only if the title presents in Org-mode source (line `#+title:some_title`).

Best regards,
Vladimir.