Update cran_env with latest envvars
build: add option for not building vignettes
install: don't build vignettes when quick=TRUE. Fixes #167
Update NEWS
Better compilating
Merge pull request #217 from wch/quick-no-vignette

install: don't build vignettes when quick=TRUE. Fixes #167
Merge pull request #223 from wch/s4-removeclass

Careful removal of S4 class references.
Be more chatty
Merge pull request #225 from hadley/better-compile

Better compilation (closes #224)
Update news
Better S4 support