Plots of continuous distributions (#2463)

* Some changes to docs

* Added plots of continuous dist

* More compact plotting for docs

Author: aasensio

docs/source/conf.py

@@ -31,6 +31,8 @@
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
+    'matplotlib.sphinxext.only_directives',
+    'matplotlib.sphinxext.plot_directive',
     'sphinx.ext.autodoc',
     'sphinx.ext.autosummary',
     'sphinx.ext.doctest',