Multiple executables in an app

[KristofferC]

Implementing this is could be done with passing a list of appname => julia_ccallable_function or something

[KristofferC]

Something like [(julia_function::String => app_name::String), ...] might be ok where by default julia_function = "julia_main" and app_name is taken from the Project.

[KristofferC]

We can do this in 2.0 by changing the existing name kwarg to create_app.