title: Change all characters in a column over multiple lines
body: <p>I'm not sure how to explain what I'd like to do, but I've seen this in Textmate and it was quite useful. Let's say I have this text:</p>
  
  <pre><code>:aa =&gt; foo,
  :ab =&gt; foo,
  :ac =&gt; foo,
  :ad =&gt; foo
  </code></pre>
  
  <p>Now I want to select all first characters of the keys (the 4 'a' in the lne) and remove them, so that the result looks like this:</p>
  
  <pre><code>:a =&gt; foo,
  :b =&gt; foo,
  :c =&gt; foo,
  :d =&gt; foo
  </code></pre>
  
  <p>Some kind of visual mode accounting columns not lines.</p>