make entry points callable as python modules

[ickc]

such that python -m toast.scripts.toast_ground_schedule -h would work or we could do

from toast.scripts.toast_ground_schedule import main
main(...)

[tskisner]

This change seems good. When building wheels through the setup.py wrapper that calls cmake, these entry points are already installed. However, when building directly with cmake, they are not installed. This small change brings the cmake install into line with the setup.py install.