pangomm: New API in pangomm 2.42

pangomm 2.46.5

New API in pangomm 2.42

Member Pango::Attribute::create_attr_fallback (bool enable_fallback)
Member Pango::Attribute::create_attr_font_features (const Glib::ustring & features)
Member Pango::Attribute::create_attr_gravity (Gravity gravity)
Member Pango::Attribute::create_attr_gravity_hint (int hint)
Member Pango::Attribute::create_attr_letter_spacing (int letter_spacing)
Member Pango::Attribute::create_attr_size_absolute (int size)
Member Pango::Attribute::create_attr_strikethrough_color (guint16 red, guint16 green, guint16 blue)
Member Pango::Attribute::create_attr_underline_color (guint16 red, guint16 green, guint16 blue)