added SQLALCHEMY_DATABASE_OPTIONS to config settings 

This allows users to customize their call to create_engine as they need to.  Specifically, this allows me to use SSL for MySQL.  I have it merge into what already exists.

<pre>class DevelopmentConfig(Config):
    SQLALCHEMY_DATABASE_URI = 'mysql+mysqldb://user:password@127.0.0.1/database'
    SQLALCHEMY_DATABASE_OPTIONS = {
        'connect_args': {
            'ssl' : {
                'key': 'ssl/mysql/client-key.pem',
                'cert': 'ssl/mysql/client-cert.pem',
                #'cert': 'ssl/mysql/ca-cert.pem'
            }
        }
    }</pre>