This function is used for all variants of r and rcmd. An argument
name is only used to refer to one kind of object, to make this possible.
convert_and_check_my_args(options)List of options.
The benefit of having a single options object is to avoid passing
around a lot of arguments all the time.
The benefit of making this object internal (i.e. that the r, etc.
functions have multiple arguments instead of a single options list),
is that documentation and usage is more user friendly (e.g. command-
completion works in the editor.