Name template arguments properly

[YarikTH]

Now error listing is very sexy:

D:\a\ureact\ureact\include\ureact/detail/var_signal.hpp(35,25): error C2059: syntax error: 'template' [D:\a\ureact\build\examples\example_complex_signals_v3.vcxproj]
          with
D:\a\ureact\ureact\include\ureact/detail/var_signal.hpp(82): message : see reference to function template instantiation 'void ureact::detail::var_signal_base<S>::set_value<std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(T &&) const' being compiled [D:\a\ureact\build\examples\example_hello_world_operators.vcxproj]
          with
          [
              S=std::string,
              T=std::basic_string<char,std::char_traits<char>,std::allocator<char>>
D:\a\ureact\ureact\include\ureact/detail/var_signal.hpp(82): message : see reference to function template instantiation 'void ureact::detail::var_signal_base<S>::set_value<int>(T &&) const' being compiled [D:\a\ureact\build\examples\example_complex_signals_v3.vcxproj]
          with
          [
              S=int,
              T=int
          [
D:\a\ureact\ureact\include\ureact/detail/var_signal.hpp(82): message : see reference to function template instantiation 'void ureact::detail::var_signal_base<S>::set_value<int>(T &&) const' being compiled [D:\a\ureact\build\examples\example_changing_multiple_inputs.vcxproj]
          with
          [
              S=int,
              T=int
              S=int,
          ]
              T=int
          ]
          ]
          ]
D:\a\ureact\ureact\include\ureact/detail/var_signal.hpp(82): message : see reference to function template instantiation 'void ureact::detail::var_signal_base<S>::set_value<std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(T &&) const' being compiled [D:\a\ureact\build\examples\example_hello_world_operators.vcxproj]
          with
          [
              S=std::string,
              T=std::basic_string<char,std::char_traits<char>,std::allocator<char>>

T, S, S, T... It's impossible to debug.