add regex support to AssertPrints
add IPython.html.nbextensions.install_nbextension

for installing files into IPYTHONDIR/nbextensions
add `ipython install-nbextension` entrypoint
add install_nbextension at top-level IPython.html
support URLs and zip/tarballs in install_extension
typo
allow installing nbextensions with symlinks
add check_nbextension
add IPython.load_extensions in js