Merge pull request #587 from knokknok/master

code changes should invalidate cache (fixes an issue when cache<3)
do not modify PATH under Mac; use kpsewhich() to find kpsewhich
markdown is imported now, so yes, just use it
play hide and seek on some internal functions from tools because R-devel will NOTE them
so that R CMD check won't see tcltk again
bump version
move \ensuremath from format_sci to the latex inline hook, so that format_sci() can be generally useful
of course I should have credited Romain for highlight
this example function is not used anywhere, so remove it
news about #587
bump version
r-devel starts to warn against non-standard top level files now
do not save display lists when cache=2; fixes #588
oops, should have only applied \ensuremath{} to sci notations
bump version
purge cache when the figure files are missing for some reason #588
bootstrap.css has moved
news for SublimeKnitr; closes #449
#588 when cache=2, I still need to preserve information about plots; instead of raw info, I save md5 digests
params is a list, so c() also works and the result will still be a list