Refactoring of method "flush!" from HTML output buffer.
Adds a newline at the end of HTML file. Updates corresponding examples.
Closes a horizontal-rule tag.
Fixes handling definition lists.
Refactoring of method "flush!" from Textile output buffer.
Slight changes.
Adds method "add_paragraph".
Merge pull request #39 from vonavi/buffer_flush

Refactoring of method "flush!" from HTML and Textile output buffer.