* Added "free software & no warranty" summary to top of COPYING.

 * tools-for-build/rtf.lisp turns COPYING into License.rtf needed
   for the installer.

 * tools-for-build/wxs.lisp generates the XML from which
   the installer is built.

 * refactor good-for-lisp pathname logic from make-target-contrib.sh
   to sbcl-pwd.sh.

 * make-windows-installer.sh builds sbcl.msi into output/,
   assuming WiX (2.0) is installed in $PROGRAMFILES/WiX or
   $WIX_PATH.

   The installer installs sbcl.exe, sbcl.core, and contribs
   into $PROGRAMFILES/Steel Bank Common Lisp/<sbcl-version>/
   by default, though the location is configurable.

   .lisp and .fasl files are associated with the installed
   SBCL, action being to start SBCL and load the file.

   The installation directory is added to PATH.

   SBCL_HOME is set to the installation directory.

   A shortcut is added to the start-menu. The shortcut refers
   to the core explicitly, and will continue to work even if
   a newer SBCL is installed.