Converter: Support for date, time and datetime. Fixes #12

Python datetime.date <-> Qt QDate <-> QML date
Python datetime.time <-> Qt QTime <-> QML time
Python datetime.datetime <-> Qt QDateTime <-> JS Date

Python C API docs for those data types:
http://docs.python.org/3/c-api/datetime.html

QML docs for those data types:
http://qt-project.org/doc/qt-5.1/qtqml/qtqml-cppintegration-data.html#qdatetime-to-javascript-date
http://qt-project.org/doc/qt-5.1/qtqml/qml-date.html
http://qt-project.org/doc/qt-5.1/qtqml/qml-time.html