Merge branch 'mlong/dosemu' into 'master'

ctrl/dosemu.conf

ctrl/sbbs.ini

exec/dosemu.ini

exec/external.bat

install/GNUmakefile

src/sbbs3/CMakeLists.txt

src/sbbs3/GNUmakefile

src/sbbs3/chk_ar.cpp

src/sbbs3/install/sbbsinst.c

src/sbbs3/sbbs_ini.c

src/sbbs3/startup.h

src/sbbs3/str_util.c

src/sbbs3/str_util.h

src/sbbs3/userdat.c

src/sbbs3/xtrn.cpp

src/sbbs3/xtrn_sec.cpp