Log Message:
Update to 1.4.20
Update LICENSE

Upstream changes:
30 May 2014: statmod 1.4.20

- Considerable work on the inverse Gaussian functions dinvgauss(),
  pinvgauss(), qinvgauss() and rinvgauss().  The parameter arguments
  are changed to mean, shape and dispersion instead of mu and lambda.
  The functions now include arguments lower.tail and log.p, meaning
  that right-tailed probabilities can be used and probabilities can
  be specified on the log-scale.  Good numerical precision is
  maintained in these case.  The functions now respect attributes,
  so that a matrix argument for example will produce a matrix result.
  Checking is now done for missing values and invalid parameter
  values on an element-wise basis.  A technical report has been
  written to describe the methodology behind qinvgauss().

- This file has been renamed to NEWS instead of changelog.txt.

- The introductory help page previously called 1.Introduction is now
  named statmod-package.

13 April 2014: statmod 1.4.19

- qinvgauss() now uses a globally convergent Newton iteration, which
  produces accurate values for a greater range of parameter values.

- glmnb.fit() now supports weights.