stats ENH: shape parameters in distribution docstrings (Trac #1581)

[scipy-gitbot]

Original ticket http://projects.scipy.org/scipy/ticket/1581 on 2012-01-06 by @josef-pkt, assigned to unknown.

the distribution docstrings use generic values for the shape parameters that often don't make much sense. In the test suite there is a list of parameters that could be used to be merged into the template.

I haven't looked at the details whether the template structure could handle this.

The numbers in the test suite are reasonable, but were initially generated by random trials and might not be the most common for each distribution. Icorrected some that looked strange in examples, but many have never been individually checked.