small doc patches

[Brian Gough]

Jochen Küpper writes:
 > | -The generator @code{gsl_rng_19937} uses the second revision of the
 > | +The generator @code{gsl_rng_mt19937} uses the second revision of the

Thanks.

 > | +articles and the NIST website. For the definition of the astronomical
 > | +unit see the JPL webpage listed below.

Is there a more definitive reference than a webpage?  I prefer to use
a printed reference if possible.

-- 
Brian Gough