title: Respect validation find messages for specific key
body: <p>How can I get a custom message for a specific key of my validation? </p>
  
  <p>For example this:</p>
  
  <pre><code>try {
      Respect\Validation\Validator::create()
          -&gt;key('foo', v::length(20))
          -&gt;key('bar', v::max(5))
          -&gt;assert([
              'foo' =&gt; 'Hello, world!',
              'bar' =&gt; 30,
          ]);
  } catch (Respect\Validation\Exceptions\ValidationException $exception) {
      $errors = $exception-&gt;findMessages([
          'key' =&gt; 'My custom message',
      ]);
      var_dump($errors, $exception-&gt;getFullMessage());
  }
  </code></pre>
  
  <p>Returns this:</p>
  
  <pre><code>array (size=1)
    'key' =&gt; string 'My custom message' (length=17)
  
  \-These rules must pass for "Array"
    |-My custom message
    | \-These rules must pass for "Hello, world!"
    |   \-"Hello, world!" must have a length greater than 20
    \-Key bar must be valid on bar
      \-These rules must pass for "30"
        \-"30" must be lower than 5
  </code></pre>
  
  <p>How can I make a custom message for the <code>foo</code> key, and separately the <code>bar</code> key?</p>