title: Specify pane percentage in tmuxinator project
body: <p>How can I specify a pane percentage in tmuxinator ?</p>
  
  <p>Eg:</p>
  
  <pre><code> project_name: ad_dev
   project_root: ~/Programming/WWW/Rails/projects/ApparelDreamDev
   rvm: ruby-1.9.2-p290@apparel_dev
   pre: SQL
   tabs:
     - editor:
         layout: main-vertical
         panes:
           - vim 75%  
           - #empty, will just run plain bash
           - top
  </code></pre>
  
  <p>eg: the vim pane would take 75% of the screen... is there a way to specify this ? or where in the documentation should I look ? Can't seem to find it anywhere.</p>