Added stubs for upcoming xsd:duration support.
Renamed test harness files for better `make` target names.
Added a mapping of header files to XSD datatypes to the README.
Added C++ class names to the README's features table.
Added links to the relevant W3C recommendations.
Added mention of xsd:dayTimeDuration and xsd:yearMonthDuration.
Added more information and missing sections to the README.
Simplified the README's top-level header title.
Added a README section on configuring static/minimal builds.
Added some pending near-term tasks to the TODO File.
Corrected the header file include directives in source files.
Implemented the xsd_*_validate() wrapper functions for plain C.
Implemented the xsd_*_canonicalize() wrapper functions for plain C.
Defined the xsd_*_value() wrapper functions for plain C.
Ensured that the xsd_*_canonicalize() wrappers catch exceptions.
Implemented the xsd::integer#as_integer() method.
Implemented the xsd_*_value() wrapper functions for plain C.
Ensured that std::cmatch is defined.
Ensured that std::regex_constants is defined.
Ensured that std::regex_constants is defined.