Add basic reading main.ini and file.ini (not all sections)

This should be enough for Nelgin to make progress with his user defaults menu
script.

Not all sections are read and parsed and there will be some extra properties
(e.g. "code" in repeated sections that don't normally have that), so the
returned objects aren't (yet) suitable for re-writing back to the *.ini files.

I also cleaned up some of the exceptions (throwing strings rather than Errors)
and removed some empty functions.