Fixed the Request concept documentation for params_t.
Added a formatter for Json::Values. It's super simple but should be there.

The Bad_Req now additionally requires a Json::Value as a param, which
represents the array given as 'params'.
Added a std::vector formatter.
Fixed a line in pif/helper.h that didn't fit the column limit.
The attach state request now accepts launch options as an object.
No more noexcept in pif.
Moved the find_formatter specialization to the helper.h.
Cleaned out pong_plugin.cpp since the request api will be changing soon.
Fixed a weird passing-to-many-types error in pif/Tuple.hpp.
New Response and Request system.
Added a base class for Invalid_Id_Exception and Invalid_Request_Exception.
New call function that expands a tuple.
Removed an unused function in engine.cpp.
Added a Req_Dispatcher.h to core/plugin to later handle the request dispatching.