pangomm: New API in pangomm 1.16

# New API in pangomm 1.16

Member Pango::Color::to_string () const

Member Pango::Context::get_base_gravity () const

Member Pango::Context::get_gravity () const

Member Pango::Context::get_gravity_hint () const

Member Pango::Context::set_base_gravity (Gravity gravity)

Member Pango::Context::set_gravity_hint (GravityHint hint)

Member Pango::FontDescription::get_gravity () const

Member Pango::FontDescription::set_gravity (Gravity gravity)

Member Pango::Layout::get_line (int line) const

Member Pango::Layout::get_lines () const

Member Pango::Layout::get_unknown_glyphs_count () const

Member Pango::Layout::is_ellipsized () const

Member Pango::Layout::is_wrapped () const