[isabelle-dev] NEWS

[Makarius]

* The Isabelle "emacs" tool provides a specific interface to invoke
Proof General / Emacs, with more explicit failure if that is not
installed (the old isabelle-interface script silently falls back on
isabelle-process).  The PROOFGENERAL_HOME setting determines the
installation location of the Proof General distribution.

* The Isabelle System Manual (system) has been updated, with formally
checked references as hyperlinks.