Johnson SU distribution

The probability density function for the Johnson SB distribution is:

.. math::

f(x, a, b) = \frac{b}{\sqrt{x^2 + 1}}
                 \phi(a + b \log(x + \sqrt{x^2 + 1}))

where :math:b > 0, :math:\phi is the pdf of the normal distribution. The following plots show the pdf and cdf:

.. image:: ../../../../tests/imgs/stats/continuous/johnsonsu/johnsonsupdf.png :align: center :width: 480

.. image:: ../../../../tests/imgs/stats/continuous/johnsonsu/johnsonsucdf.png :align: center :width: 480