finalizing documentation for @jules32's gapfill_georegions

woops, needed to fetch your changes first. now for real...

```
library(devtools)
load_all()
document()
``
This processes the commented code with roxygen2 and updates the R documentation files, ie `man/gapfill_georegions.Rd`.
Merge branch 'master' of github.com:bbest/ohicore