initial date printer
Fixed gregorian date printer to correctly match the type and return string in standard fashion. Added check for uninitialized state
Merge branch 'gregoriandate'
Merge branch 'master' of https://github.com/ruediger/Boost-Pretty-Printer
Added support for boost::posix_time::ptime

This prints the time as a raw number which is not interpretable for humans. If anyone knows how to convert this sensibly to a readable (UTC?) time, please let me know.
Merge pull request #5 from brokenn/ptime

Add rudimentary support for boost::posix_time::ptime