Use open() so the file handler is closed OK
Use context manager to autoclose fd after creating mmap
Add copyright and licensing headers, and docstrings.
Add basic standard balloon stages factory.
Merge pull request #6 from adamgreig/close_fd

Use open() so the file handler is closed OK
Merge pull request #8 from adamgreig/copyright

Copyright headers etc
Merge pull request #9 from adamgreig/abstract_models

Abstract models