Return the GitHub client, cached into __context__ for performance

def _get_client(profile):
    '''
    Return the GitHub client, cached into __context__ for performance
    '''
    token = _get_config_value(profile, 'token')
    key = 'github.{0}:{1}'.format(
        token,
        _get_config_value(profile, 'org_name')
    )

    if key not in __context__:
        __context__[key] = github.Github(
            token,
            per_page=100
        )
    return __context__[key]