Implement dynasegs, from Eternity

src/CMakeLists.txt

src/Makefile

src/hardware/hw_bsp.c

src/hardware/hw_main.c

src/m_dllist.h

src/p_maputl.c

src/p_maputl.h

src/p_mobj.c

src/p_polyobj.c

src/p_polyobj.h

src/p_setup.c

src/p_setup.h

src/p_spec.c

src/r_bsp.c

src/r_defs.h

src/r_dynabsp.c

src/r_dynabsp.h

src/r_dynseg.c

src/r_dynseg.h

src/r_segs.c