Return a list of (name, value) tuples for each option in a section.
All % interpolations are expanded in the return values, based on the
defaults passed into the constructor, unless the optional argument
`raw` is true. Additional substitutions may be provided using the
`vars` argument, which must be a dictionary whose contents overrides
any pre-existing defaults.
The section DEFAULT is special.
3.8: Items present in vars no longer appear in the result. The previous behaviour mixed actual parser options with variables provided for interpolation.