- updated documentation wrt. new repository layout
- temporarily switched off Homebrew --HEAD building (can only be switched on after release)
- set copyright date to 2018
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>`.
