swapped AggregateLayers.R with gapfill_georegions.R and removed sqldf dependency. resolves #81. in process with #29.
dropped zoo requirement and added ddplyr
dropped zoo requirement and added dplyr
Merge branch 'master' of https://github.com/bbest/ohicore
fixing NAMESPACE
Merge pull request #91 from bbest/master

added gapfill_georegions and dropped sqldf and zoo requirements