make output of timestamp optional
update list of required LaTeX packages (@sietse)
union merge for NEWS.md [ci skip]
Merge branch 'master' into make_timestamp_optional
add section to NEWS
Merge pull request #80 from yihui/make_timestamp_optional

Make output of timestamp optional
attempt to reduce merge conflict
Merge branch 'master' into 68-lwd

Conflicts:
	src/tikzDevice.c