PK stuff arising from last PR

[bbolker]

add appropriate cross-references to https://cran.r-project.org/view=Pharmacokinetics ! add Matt Fidler as contributor.

[mattfidler]

I think that I am already listed as a contributor (though it says Matthew instead of Matt). Thanks for keeping me in mind, though.

[bbolker]

Do you prefer Matt?

[mattfidler]

I usually use Matthew for publishing, so this is fine with me.