fixes #874: create figure directories recursively for the engines tikz and dot
closes #581: add a filter function for spell checking
add a news item for #581, although I did not really add knit_filter() to the vignette engines
roxygenize
closes #621: a new function spin_child() to spin child R scripts
roxygenize
fixes #654: switch the order of alignment and sub fig, so sub figures can be aligned correctly
split aniopts and paste the options with spaces; then pass the options to <video>
closes #712: add a new hook_ffmpeg() so that one can define the video format

e.g. opts_knit$set(animation.fun = knitr:::hook_ffmpeg)
bump version