Don't call logging.basicConfig() in library code - #22

Logging should be configured by the application, not by libraries it
uses. Libraries should just get a logger and log to it.

Fixes #21

For another concrete problem caused by calling logging.basicConfig() in the library, import telegram changes the meaning of the following program:

import logging
import telegram

log = logging.getLogger(__name__)

if __name__ == '__main__':
    logging.basicConfig(level='DEBUG')
    log.debug("this should be printed, but will not be "
        "unless you comment out 'import telegram'")