Potential workaround for #136

doc/help.md

@@ -0,0 +1,49 @@
+## error: 'to_string' is not a member of 'std'
+
+This is an error that might come up when using certain GNU based compilers, including:
+
+* MinGW 4.7, 4.8
+* Android NDK
+* ...
+
+This is not an issue with this json tool, but rather with the compiler itself. Here's how I fixed it, thanks to [this page](http://tehsausage.com/mingw-to-string). I do not guarantee that this will work, only that it worked for me.
+
+### mingw/include/wchar.h, mingw/include/stdio.h
+
+(This same snippet needs replacing in two header files)
+
+```
+-/* These differ from the ISO C prototypes, which have a maxlen parameter like snprintf.  */
+-#ifndef __STRICT_ANSI__
+-_CRTIMP int __cdecl __MINGW_NOTHROW    swprintf (wchar_t*, const wchar_t*, ...);
+-_CRTIMP int __cdecl __MINGW_NOTHROW    vswprintf (wchar_t*, const wchar_t*, __VALIST);
+-#endif
++__CRT_INLINE int __cdecl __MINGW_NOTHROW swprintf (wchar_t* buffer, size_t count, const wchar_t* format, ...)
++{
++  __builtin_va_list argptr;
++  __builtin_va_start(argptr, format);
++  return _vsnwprintf(buffer, count, format, argptr);
++}
++
++__CRT_INLINE int __cdecl __MINGW_NOTHROW vswprintf (wchar_t* buffer, size_t count, const wchar_t* format, __VALIST argptr)
++{
++  return _vsnwprintf(buffer, count, format, argptr);
++}
+```
+
+### mingw\lib\gcc\mingw32\4.7.0\include\c++\mingw32\bits\os_defines.h
+
+This preprocessor flag needs to be removed
+
+```
+-#define _GLIBCXX_HAVE_BROKEN_VSWPRINTF 1
+```
+
+### MinGW\lib\gcc\mingw32\4.8.1\include\c++\mingw32\bits\c++config.h
+
+This may or may not be necessary, but if so, then makefiles will require `-std=gnu++11` too.
+
+```
+-/* #define _GLIBCXX_USE_C99 1 */
++#define _GLIBCXX_USE_C99 1
+```

src/json.hpp

@@ -70,25 +70,6 @@ Class @ref nlohmann::basic_json is a good entry point for the documentation.
     using ssize_t = SSIZE_T;
 #endif
 
-// workaround for Android NDK (see https://github.com/nlohmann/json/issues/136)
-#ifdef __ANDROID__
-namespace std
-{
-template <typename T>
-std::string to_string(T v)
-{
-    std::ostringstream ss;
-    ss << v;
-    return ss.str();
-}
-
-inline long double strtold(const char* str, char** str_end)
-{
-    return strtod(str, str_end);
-}
-}
-#endif
-
 /*!
 @brief namespace for Niels Lohmann
 @see https://github.com/nlohmann