Missing directives in NAMESPACE for stdEr and deviance S3 methods.

This causes and error when calling the `stdEr()` generic function (no applicable method for 'stdEr' applied to an object of class "admb"), and results in `NULL` being returned by a call to `deviance()`.

I have added the directives to the NAMESPACE as well as updating the associated roxygen code.

(I note that these directives _are_ included in the NAMESPACE for the version on CRAN, were they removed intentionally for some reason? If so, ignore this!)