0.15

This releases adds support for gcc 6 (along with continued support for gcc 4.6, 4.7, 4.8, 4.9 and 5).

Additionally, this release contains the following improvements (contributed by Tom Tromey; thanks Tom):

• document gcc.PLUGIN_FINISH_TYPE
• document gcc.EnumeralType; add ‘values’ attribute
• add unqualified_equivalent to gcc.Type subclasses
• preserve qualifiers when adding more qualifiers
• fix include for gcc 4.9.2
• handle variadic function types