The documentation mismatched the actual code.

needed for VS2015.3 with /std:c++latest

As I learned in https://github.com/melpon/wandbox/issues/209, this
library is already installed at Wandbox, so we need to adjust the
examples to use `#include "json.hpp"` insteas of `#include <json.hpp>`.

std::setw needs the iomanip header (at least with GCC).

The example with the size() operator is bad: using operator[] already
changes the size of the object. The fix makes it clearer.

These files were never meant to be versioned.

Taken from
https://github.com/travis-ci/docs-travis-ci-com/pull/746/files.

To test a fix for issue #464 (not yet implemented), we first need to
have  an MSVC build with “/permissive- /std:c++latest /utf-8”.

This implementation forwards the iterators to std::map::insert.

We totally forgot to implement the comparison operators other than ==
and != for scalar types. Consequently, comparing a JSON value with a
scalar type led to compile errors.

add enum class default conversions

Properly pop diagnostics

The implementation is non-standard. Deprecation allows a simpler API in
the future without removing any features.

NaN values never compare equal to themselves or to other NaN values.

https://blog.travis-ci.com/2017-03-28-xcode-83-ga-is-here

We now only demand our exceptions to be is_nothrow_copy_constructible
if std::runtime_exception is.

The solution with a std::runtime_error member is more elegant. It
allows to have std::exception as base class again. However, I still
have no idea why GCC thinks the copy constructor may throw...

To have nothrow-copy-constructible exceptions, we inherit from
std::runtime_error which can cope with arbitrary-length error messages.
Intermediate strings are built with static functions and then passed to
the actual constructor.