bin/cygbuild.sh: (CygbuildInstallExtraBinFiles): add support for bin/FILE.cyginstdir install instructions

Signed-off-by: Jari Aalto <jari.aalto@cante.net>
bin/lib/cygbuild.pl: Fix POD
make doc

Signed-off-by: Jari Aalto <jari.aalto@cante.net>