Setup the default settings.

def setup_git(pelican):
    """Setup the default settings."""
    pelican.settings.setdefault('GIT_CACHE_ENABLED', False)
    pelican.settings.setdefault('GIT_CACHE_LOCATION',
                                '/tmp/git-cache')

    # Make sure the cache directory exists
    cache_base = pelican.settings.get('GIT_CACHE_LOCATION')
    if not os.path.exists(cache_base):
        os.makedirs(cache_base)