Handle configuration file versions.

version_info was renamed PICARD_VERSION
version_string was renamed PICARD_VERSION_STR
short version string is stored in PICARD_VERSION_STR_SHORT (for display)

Hooks can be created to handle upgrades (ie. options renaming), see config.register_upgrade_hook() and config.run_upgrade_hooks()
PEP8 compliance fixes
Merge pull request #131 from zas/update_config_2

Handle configuration file versions