Implement ImageDataIterator and stablize the data interface API
Adapt the ThreadBuffer of CXXNET into DataFetcher
Replace cxxnet thread with boost::thread in the DataFetcher
Replace CXXNET Semaphore with boost::mutex and condition_variable

Why has class semaphore disappeared?
http://www.boost.org/doc/libs/1_31_0/libs/thread/doc/faq.html#question10