Update databases.Rmd
Update top-n.R

Fix Issue #426 by using `missing` which does not evaluate it's argument(s)
Make ruler width customisable
Update data.r

This variable is never used, so I believe it can be safely removed
export sample_n/frac methods for grouped_df
Update group-by.r
Fix for #475
Missed to return data
Fail early when empty pattern is provided to select_vars

The current default behaviour of select_vars, with sub
functions `starts_with`, `ends_with`, `contains` and
`matches`, when provided with a character pattern of
length zero, is to return all columns of the tbl. This commit
changes that default behaviour: now these functions fail
early, selecting nothing and telling the user that
an empty pattern was provided.
Re-export `%>%` without a copy

Fixes #488
correct typo in ?manip
correct small typo in introduction vignette
fix typos in ?tbl_df
grammar-o
Merge pull request #510 from craigcitro/patch-1

grammar-o
Merge branch 'master' of github.com:hadley/dplyr
Pass ... onto base functions. Closes #507
Merge pull request #500 from ncarchedi/master

Correct a few scattered typos
Merge pull request #496 from jimhester/pipe_export

Re-export `%>%` without a copy
Update docs