jus tested rmarkdown, and this does not work because of the leading white spaces

Pandoc may treat these spaces as the <pre></pre> syntax (#735)
fixes #735: do not use a PNG snapshot

well, this does not really fix the problem; the root problem is from Pandoc
bump evaluate version
use relative font size for the docs column in the docco classic style
the custom rendering function should accept an `options` argument, which is a list of current chunk options

knit_print() also has to have an `options` argument
add chunk options out.width.px/out.height.px (figure size in pixels instead of inches)
an ugly "fix" due to Pandoc's inappropriate treatment of escaped double quotes
roxygenize
bump version