Workaround MSVC bug; converting C strings to bool (#177)

On MSVC passing 'const char*' assigns a 'bool' to std::variant instead
of std::string. A non-template overload does prevent this, but will
catch '0' as nullptr.

This can be removed once C++20 is used.

include/Point.h

@@ -33,6 +33,7 @@
 #include <chrono>
 #include <variant>
 #include <deque>
+#include <type_traits>
 
 #include "influxdb_export.h"
 
@@ -55,6 +56,12 @@ namespace influxdb
         using FieldValue = std::variant<int, long long int, std::string, double, bool, unsigned int, unsigned long long int>;
         Point&& addField(std::string_view name, const FieldValue& value);
 
+        template <class T, class = std::enable_if_t<std::is_same_v<T, const char*>, int>>
+        Point&& addField(std::string_view name, T value)
+        {
+            return this->addField(name, std::string{value});
+        }
+
         /// Generates current timestamp
         /// \deprecated Will be removed in v0.8.0
         [[deprecated("getCurrentTimestamp() will be removed in v0.8.0")]] static auto getCurrentTimestamp() -> decltype(std::chrono::system_clock::now());