title: Julia - MLJ - ERROR: UndefVarError: train_test_pair not defined
body: <p>I'm new to Julia and currently trying the <a href="https://alan-turing-institute.github.io/MLJ.jl" rel="nofollow noreferrer">MLJ</a> package. More precisely, I try to use some resampling strategy outside of the <code>evaluate</code> functions.</p>
  <p>However the following simple lines :</p>
  <pre><code>using MLJ
  
  cv = CV()
  train_test_pairs(cv, 100)
  </code></pre>
  <p>raise <code>ERROR: UndefVarError: train_test_pairs not defined</code></p>
  <p>Is there something obvious I'm missing? I think it's because the <code>train_test_pairs</code> methods are not exported by the package, is that correct? If yes, what is the rationale behind this choice?</p>