DEBUG in common.py dealt as str after loaded from config file

[oplier]

Hello Charles,

In my environment (Python 2.7), I found that variable DEBUG is recognized as str type instead of Bool type, after setting debug loaded from config file (".git\gitcc"): https://github.com/charleso/git-cc/blob/9db20378537ac92b96bad58d5e3d511a696884f3/git_cc/common.py#L228

Then when calling function debug, regardless of the setting value, it will enter the if case and do the print action: https://github.com/charleso/git-cc/blob/9db20378537ac92b96bad58d5e3d511a696884f3/git_cc/common.py#L72-L74

[charleso]

@oplier Thanks for the issue, and I'm sorry the git-cc code is so horrible. :( I'm not really actively maintaining this, but if you send me a PR I will happily merge if it looks sensible.