Move netcode files to a new folder

src/Makefile

src/Sourcefile

src/android/i_net.c

src/blua/liolib.c

src/command.c

src/d_main.c

src/deh_soc.c

src/deh_soc.h

src/doomstat.h

src/dummy/i_net.c

src/f_finale.c

src/filesrch.c

src/filesrch.h

src/g_demo.c

src/g_game.c

src/g_input.c

src/hardware/hw_main.c

src/hu_stuff.c

src/i_time.c

src/lua_baselib.c