Attached particle spawners

doc/lua_api.txt

src/client.h

src/content_sao.cpp

src/environment.cpp

src/environment.h

src/network/clientpackethandler.cpp

src/particles.cpp

src/particles.h

src/script/lua_api/l_particles.cpp

src/server.cpp

src/server.h

src/serverobject.cpp

src/serverobject.h