group_by the data when vectorized is on
add vectorized option and reformat
call generic again in map or reduce in case we are using a tbl_df
always return a data frame
added vectorization to extension pack for dplyr
shorten
merge from vectorized-groups

Merge branch 'vectorized-groups' into dev

Conflicts:
	docs/revo-blog/post.Rmd
	docs/revo-blog/post.md