MS Visual Studio "/Zc:wchar_t-" compiler parameter support added

[slavanap]

If /Zc:wchar_t- compiler parameter is specified, then wchar_t is defined as
typedef unsigned short wchar_t;
Thus, this leads to conflict in template definition in format.h

You can verify it in any Visual Studio project with spdlog with

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:wchar_t-")

reference: https://msdn.microsoft.com/ru-ru/library/dh8che7s.aspx

[gabime]

format.h is the cppformat library. Please issue the merge there

[slavanap]

Ok. Thank you for the tip.
I've already submitted it.

[slavanap]

@gabime One more thing, because I don't know how to submit pull request to wiki page.
https://github.com/gabime/spdlog/wiki/1.-QuickStart

namespace fmt should be specified for custom operator<<, otherwise it doesn't compile under MSVS 2015.

class some_class {};
namespace shared {
    std::ostream& operator<<(std::ostream& os, const some_class& c) {
        return os << "some_class";
    }
}
using namespace shared; // not necessary

namespace fmt {
    using namespace shared;
}

void custom_class_example() {
    some_class c;
    auto console = spd::stdout_logger_mt("console");
    console->info("custom class with operator<<: {}..", c);
    console->info() << "custom class with operator<<: " << c << "..";
}