add missing context type definitions + BOOST_SPIRIT_INSTANTIATE_UNUSED macro to instantiate `parse_rule` with `boost::spirit::x3::unused_type` attribute
add missing context type definitions + BOOST_SPIRIT_INSTANTIATE_UNUSED macro to instantiate `parse_rule` with `boost::spirit::x3::unused_type` attribute

mapnik/mapnik,tomhughes/mapnik,naturalatlas/mapnik,tomhughes/mapnik,lightmare/mapnik,naturalatlas/mapnik,tomhughes/mapnik,lightmare/mapnik,mapnik/mapnik,naturalatlas/mapnik,mapnik/mapnik,lightmare/mapnik,naturalatlas/mapnik,tomhughes/mapnik,mapnik/mapnik,lightmare/mapnik