Merge pull request #103: Open HTML in split & Mediawiki converter

In this merge commit I'm making a couple of minor changes:

 - The `---` sequence is now used as a horizontal divider in the
   Mediawiki syntax converter.

 - The changes to xolox#notes#html#view() created a temporary file even
   when the HTML was shown in a Vim split window, now the temporary file
   is only created when it needs to be passed to a web browser.

 - I changed some wrong indentation, removed some unused code (the
   counter variable) and renamed some private variables
   (s/hilight/highlight/g) and added word boundaries to the
   TODO/DONE/XXX matching in the file mediawiki.vim.

 - No trailing empty lines are added when a note is converted to
   Mediawiki syntax (there were in the pull request, but without context
   or explanation so I'd rather keep the Markdown, HTML and Mediawiki
   converters consistent).
Easy customization of new note template (also from command line)

This was added to enable simple integration with
tools like sup (https://github.com/ceocoder/sup)