Candidate for 0.2 with diff support for all objects

FIXED:
- rework of NmapHost and NmapService API
- added __hash__, id and get_dict() for common Nmap Objects
- added NmapDiff class
- full rework of unittests
- NmapParser now supports parsing from file
- NmapParser is able to handle nmap XML portions
- added import in reports

TODO:
- Add Sphinx DocStrings
- NmapParser should be able to be fully generic and return Objects
- NmapParser should not need a XML root
- NmapReport export(), import() should support plugins for csv (multi-format) mongodb, mysql, ...
- support iterators for NmapReport::scanned_hosts
- refactory NmapHost() constructor
- add support for parsing os version and banner of port
- expose a clear API for NmapHost, NmapService and NmapParser
- add support for 'resume' capability
- review thread management for NmapProcess