cIniFile cleanup

This provides a cleaner API for cIniFile, both in the C++ code and the Lua API.

The object doesn't keep track of the filename anymore, the file is explicitly specified for ReadFile() and WriteFile() functions.

The functions were renamed to provide more explicit names and remove overrides: KeyComment() -> AddKeyComment() / GetKeyComment()

Some obsolete functions were removed.

All the numeric values use the int type, instead of mixing longs with unsigneds and ints and size_t-s

NOTE: This change WILL break existing plugins that use cIniFile. Fixing those plugins is easy enough, but still it's a breakage. Go with it?