title: Define a 4-parameters Beta prior in pymc3
body: <p>I want to do a Bayesian analysis using pymc3.  One of my parameters has a Beta distribution with a=28.78, b=0.98, loc=-0.22, scale= 0.32. Does anyone know how to define a 4-parameters Beta distribution inside the pymc3 model? Something like:</p>
  <pre><code>with pm.Model() as model_g:
      n=pm.Beta(‘n’, 28.78, 0.98, -0.22, 0.32)
  </code></pre>