Updated example.conf.
Refactored main.py.

Changes include:
- moved exit codes to constants
- reordered the configuration getters to reflect the ordering of the
  configuration file
- new class BackupParameters that contains all parameters necessary to
  create a new backup
Merge branch 'refactoring'

Conflicts:
	src/main.py
Fixed pep8 warnings.
Simplifies get_section() by calling get_sections().
Trimmes example.conf to 79 characters and adds notes.
Adds pep8 to the tests, tests fail if pep8 complains.