the breakurl package has been causing me trouble for long, so just remove it
skip the PDF manual and do not rebuild vignettes, so that we can avoid installing texlive

hopefully this can reduce a large portion of travis ci time

also added r-cran-rgl; I forgot why I did not add it; there might be a reason
if the input file does not exist in rocco(), just return
for Travis, use --no-build-vignettes for R CMD build
roxygenize
do not install the package, since `make install` will build vignettes by default
sigh, now Simon's RForge does not have upquote.sty either
the tags should not be empty, e.g. !{}url! does not work; neither should the caption, e.g. !url()!

#623
cosmetic
use CSS classes separated by spaces instead of _ (#623)
remove the check for output_asis() in every single output hook; do it in wrap.character() instead
partially reverted f0ee3f9 in #635: this only affects old-style figures, but in that case, users are still free to use $\Sexpr{number}$

\ensuremath{} was used only for the sake of safety for sci notations; it also makes sense for negative numbers and infinity symbols, but seems to be an overkill to be applied to all numbers

after re-compiling knitr-examples, there are a bunch of git differences; now they are gone
introduced a bug while fixing #636, and fortunately it was caught by example 091
should be more careful about figure alignment: fig.align must be converted to CSS
block code should not start with a new line
make sure all lines will be pasted into one string
do not use @@ on inline expressions, and @(knitr inline)@ does not really work (#623)
uses css classes knitr plot caption instead of a single knitr_plot_caption
make sure blocks next to a figure are separated by \n\n
add textile to description and reflow it