Merge upstream commits and resolve conflicts

CONTRIBUTING.md

@@ -62,6 +62,7 @@ Please understand that I cannot accept pull requests changing only file `src/jso
 - The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.8 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
 - Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
 - Please refrain from proposing changes that would **break [JSON](http://json.org) conformance**. If you propose a conformant extension of JSON to be supported by the library, please motivate this extension.
+- Please do not open pull requests that address **multiple issues**.
 
 ## Wanted
 

README.md

@@ -388,7 +388,7 @@ I deeply appreciate the help of the following people.
 - [406345](https://github.com/406345) fixed two small warnings.
 - [Glen Fernandes](https://github.com/glenfe) noted a potential portability problem in the `has_mapped_type` function.
 - [Corbin Hughes](https://github.com/nibroc) fixed some typos in the contribution guidelines.
-- [twelsby](https://github.com/twelsby) fixed the array subscript operator.
+- [twelsby](https://github.com/twelsby) fixed the array subscript operator and an issue that failed the MSVC build.
 
 Thanks a lot for helping out!
 

src/json.hpp

@@ -43,7 +43,9 @@ Class @ref nlohmann::basic_json is a good entry point for the documentation.
 #include <cassert>
 #include <ciso646>
 #include <cmath>
+#include <cstddef>
 #include <cstdio>
+#include <cstdlib>
 #include <functional>
 #include <initializer_list>
 #include <iomanip>
@@ -53,6 +55,7 @@ Class @ref nlohmann::basic_json is a good entry point for the documentation.
 #include <map>
 #include <memory>
 #include <sstream>
+#include <stdexcept>
 #include <string>
 #include <type_traits>
 #include <utility>

src/json.hpp.re2c

@@ -43,7 +43,9 @@ Class @ref nlohmann::basic_json is a good entry point for the documentation.
 #include <cassert>
 #include <ciso646>
 #include <cmath>
+#include <cstddef>
 #include <cstdio>
+#include <cstdlib>
 #include <functional>
 #include <initializer_list>
 #include <iomanip>
@@ -53,6 +55,7 @@ Class @ref nlohmann::basic_json is a good entry point for the documentation.
 #include <map>
 #include <memory>
 #include <sstream>
+#include <stdexcept>
 #include <string>
 #include <type_traits>
 #include <utility>