User Defined Literals and performance improvements

• I added a C++ string UDL so you can parse a hard-coded GraphQL query or schema with "..."_graphql, much like the graphql function in Relay which instructs the relay-compiler to preprocess queries embedded in JS/JSX (or TS/TSX for TypeScript).
• I made some improvements to the tests to cache more between tests in the test class/fixture so there's less work in the per-test Setup/Teardown.
• The RapidJSON calls are optimized to avoid excessive memory copies between separate documents at runtime in the service. Pretty much all of the rapidjson::Value objects included in the results document should be constructed in place using the target document's own allocator.