Support of Python 3

Hi,

Thanks for your wonderful package, I use it for running sets of simulations on clusters. I needed Python 3 support, so I implemented it.

The code has been tested on 2.7.3, 3.2.4 and 3.3.1 (all unit tests pass), on OS X. It is far from elegant or optimal, and it may adversely affect performance. The main changes are : 
1. print statements
2. the str/bytes conundrum, of importance for hashes.
3. the iteritems/items for dict.

Optimization may be possible.