template version with re2c scanner

[nlohmann]

• Changed: In the generic class basic_json, all JSON value types (array, object, string, bool, integer number, and floating-point) are now templated. That is, you can choose whether you like a std::list for your arrays or an std::unordered_map for your objects. The specialization json sets some reasonable defaults.
• Changed: The library now consists of a single header, called json.hpp. Consequently, build systems such as Automake or CMake are not any longer required.
• Changed: The deserialization is now supported by a lexer generated with re2c from file src/json.hpp.re2c. As a result, we follow the JSON specification more strictly. Note neither the tool re2c nor its input are required to use the class.
• Added: The library now satisfies the ReversibleContainer requirement. It hence provides four different iterators (iterator, const_iterator, reverse_iterator, and const_reverse_iterator), comparison functions, swap(), size(), max_size(), and empty() member functions.
• Added: The class uses user-defined allocators which default to std::allocator, but can be templated via parameter Allocator.
• Added: To simplify pretty-printing, the std::setw stream manipulator has been overloaded to set the desired indentation. Pretty-printing a JSON object j is as simple as `std::cout << std::setw(4) << j << '\n'.
• Changed: The type json::value_t::number is now called json::value_t::number_integer to be more symmetric compared to json::value_t::number_float.
• Removed: The key() and value() member functions for object iterators were nonstandard and yielded more problems than benefits. They were removed from the library.

[coveralls]

Coverage remained the same at 100.0% when pulling c8c49da on template into c4d7485 on master.