Improve blog posting from the command line

[garrett]

Make a better command to make a blog post, with the following:

1. Template support, possibly build on the new template support in middleman-blog:
   http://middlemanapp.com/basics/blogging/#generating-articles
   (Using blog.new_article_template)
2. Use $USER as the default author (with an override somehow)
3. Open in $EDITOR (falling back to xdg-open if $EDITOR doesn't exist) and launch xdg-open $URI_TO_ENTRY