Support settings files on Python 2

Previously, settings files would be silently ignored on Python 2.x unless the optional PyPI configparser package was installed.

This commits tries the newer import and falls back to the legacy 2.x stdlib name. Additionally, it no longer silently hides errors when a config file exists but is not readable for some reason as the user should know when the config they intended to use cannot be loaded.
Merge pull request #76 from acdha/patch-1

Support settings files on Python 2.x
Merge tag '2.4.1' into develop

2.4.1
Add test for issue #77
Fix issue 77: Add support for changing the default section for unknown imports
Update documentation
Merge pull request #78 from timothycrosley/feature/fix-issue-77

Feature/fix issue 77
Support for printing a diff of proposed changes instead of modifying the file
Add documentation for diff command
Small fix
Merge pull request #79 from timothycrosley/feature/fix-issue-74

Feature/fix issue 74
Bump version to 2.5.0
Merge branch 'release/2.5.0'