Removes the breaking libosrm API change by replacing the
use of variant response type with method overloading.
This has the added benefit of being explicit about the supported
response types for each libosrm API method.
To fix#2193 prefix_length member variable has been added to ParsedURL
that is set to the length of "/service/version/profile/" prefix
when the prefix is accepted by the parser.
Also BOOST_FUSION_ADAPT_STRUCT for osrm::server::api::ParsedURL
has been moved from header to url_parser.cpp to speed up compilation
of CUs that do not use the fusion adaption.
