Wrap resource concept.

[ben-crowhurst]

Currently we move resource data around via a std::multimap. This has worked to date however we are finding lots of duplicated String::to_string/to_bytes, find... calls.

Reduce duplication with a light-weight wrapper.

Resource resource( const std::multimap< std::string, std::string >& values );
resource.set( "name", string or bytes value );
resource.get( "name" ); //returning string or bytes value.