support synchronous `put` operation

[davidAtInleague]

To fix #13, this enables a "synchronous" mode for the put operation. A configuration can now look like:

this.cache.connections[ "x" ] = {
    class : 'lucee.extension.io.cache.redis.simple.RedisCache',
    bundleName : 'redis.extension',
    bundleVersion : '3.0.0.<x>',
    storage : true,
    custom : {
        "password" : "",
        "port" : "1234",
        ...
        "synchronousPut": true,
    }
};

Very high confidence this fixes the reported race condition, but I haven't done any performance regression testing to see how this pans out in the real world. However, the new option is entirely opt-in, so any regressions would be new behavior that people have to sign up for via configuration.

[CLAassistant]

All committers have signed the CLA.

[davidAtInleague]

closed in favor of #16