Rev deps

This will read the DESCRIPTION file and check the reverse dependencies according to the name of the package.

Probably should do this with a flag, like you do with LaTeX.  (I want it to be done every time, because CRAN requires that we check all reverse dependencies.)

-Barret
I think you could probably simplify this -- unless I'm missing something, the R code here should be the same thing as

    'library(devtools); revdep_check(as.package("."))'

This also lets you drop all the business around `stringr`, I think?