autocorres: update release tool for Isabelle2018

Note that we have removed the LIB_FILES manifest and no longer intend
to maintain it manually. Instead, we just extract the entire Lib and
CLib sessions from the L4.verified repository. This means that the
next AutoCorres release will have some unneeded theories and a couple
of files with GPL licenses.

autocorres: Setup release scripts for new directory structure.