error checks for private/public symbols in modules

[felixangell]

we need to make sure that we are only referencing symbols in modules that have been made public i.e are capitalized.

an interesting thought/assumption:

module_name.some_module_member

rather than checking if some_module_member is public, we know it's private since it's in lowercase... we could then check to see if the member exists and then complain?