Make it possible to execute an rc file in the initialiser

[mlang]

I am looking for a way to execute an rc file during initialisation phase.

Right now, all I can do is call "command" manually, but there is no
way to invoke the options parser manually. I'd have to reimplement options
parsing myself, which seems wrong.

The goal is to have something like .ghci, where :commands would also work as expected.