Differentiate between the input type, as specified in the json configuration
file, and the internal native type used to store data. This is a many-to-one
mapping, where e.g. both the input types STRING and RAW_STRING map to the
internal datatype std::string.
Additional changes:
- Have removed several ParserItem() constructors.
- The size_type::SINGLE is default for a ParserItem, and not set explicitly in
the generated ParserKeywords.cpp file.
- Have removed a call to boost::lexical_cast<> - just use std::to_string()
