Add a newline right before the headlines for readability.

Having at least a newline before the section title is much readable
than concatnated with previous section.  Add a newline for now.
Add inline text format support

Add the following text format support:

 from org        | to pukiwiki
-----------------+------------------
 bold            | bold
 italic          | italic
 code / verbatim | none (pukiwiki does not have any)
 underline       | underline
 strike-through  | strike-through