Throwing error when using invalid topic name

[nikeee]

The library does not throw any exception or error when using a topic name that is not valid.
The only legal characters in a topic are:
a-z, A-Z, 0-9,., _ and -
See: https://github.com/apache/kafka/blob/0.9.0/core/src/main/scala/kafka/common/Topic.scala#L25
This character constraint exists due to this.

Maybe it would be a good idea to inform the library user that the topic is not valid. I just spent an hour of debugging because a topic contained a /. Therefore, the connection timed out with a Failed to update metadata after %s secs. error which does not seem to be related on first sight.

[nikeee]

Fixed in #1238