#35 compilation issues with 64-bit and newer C++ in VS 2017

[Nat Brown]

issues when compiling for 64-bit with Visual Studio 2017, e.g. cmake -G "Visual Studio 15 2017 Win64" -DOpenCV_DIR=<path_to_opencv_3.4.1>/build/x64/vc15/lib

• minor: many build warnings about conversion due to size_t vs uint64_t and uint32_t and unsigned. these warnings can be fixed without impacting older VS and C++ versions and 32-bit builds
• major: dictionary.h defines MarkerMap:::insert as _code_id.insert(std::make_pair(code, id)); - this triggers an obscure error because of the type difference to the latest c++ between int and uint16_t - an explicit cast is at least needed, _code_id.insert(std::make_pair(code, (uint16_t)id));, or the signature of insert could be changed to require callers provide uint16_t.

[Nat Brown]

also when building from a strict project with "treat warnings as errors" project, in markerdetector.h aruco::MarkerDetector::_toStream needs to use uint32_t s=(uint32_t)strg.size(); instead of uint32_t s=strg.size();. that seems to be the only type conversion warning which blocks strict consumers of the API