Update between.cpp

typo
Set the row.names by the first non-short length

Before this was always using the first length, which resulted in the
data.frame being truncated if the first argument was a length 1 vector
to be recycled.

Fixes #680
Add note to news
Simplify logic for NA length
context is not capitalized
Add a few more data_frame tests

This is mostly to get Travis to retry the build.
Fix extraneous parenthesis.
Extra whitespace

hopefully travis will run correctly this time :-/
doc fix.
doc fix
Update docs.
additional case handle of all NA columns closes #493
-pedantic finding from #722
some windows love. #722
oops
needs being const [ci skip]
as suggested by -Wparentheses on #windows
some more care in row_number. closes #781
Prune travis of now unnecessary packages
Print at most 20 rows

Closes #710