Replace ContextValue with std::any

[ben-crowhurst]

1. Investigate the use of std::experimental::any as a replacement for ContextValue.
2. If during compile time its not available fallback to boost::any.

[ben-crowhurst]

The following approach has been suggested for 5.0.

Session session;
SessionData data = session.get_data( );
int value = data.get( "max-age", 0 );

Completely removing the requirement of a std::any datatype and exchanging the concept with a Request style template.