make entry points callable as python modules

such that `python -m toast.scripts.toast_ground_schedule -h` would work
or we could do
```py
from toast.scripts.toast_ground_schedule import main
main(...)
```

src/toast/scripts/CMakeLists.txt

@@ -23,6 +23,7 @@ set(ENTRY_POINTS
 foreach(pyscript ${ENTRY_POINTS})
  string(REPLACE ".py" "" outscript "${pyscript}")
  install(PROGRAMS "${pyscript}" DESTINATION bin RENAME "${outscript}")
+ install(FILES "${pyscript}" DESTINATION ${PYTHON_SITE}/toast/scripts)
 endforeach()
 
 install(FILES