Simple java consumer

Creates a simple blocking java consumer.  It is expected that this code is executed inside of a thread (or something similar)


```ruby
# $bundle exec jruby hermann_test.rb


require 'hermann'
require 'hermann/provider/java_simple_consumer'
require 'hermann_jars'

zookeeper = "localhost:2181"
groupId   = "group1"
topic     = 'test'

example = Hermann::Provider::JavaSimpleConsumer.new(zookeeper, groupId, topic)

example.get_messages do |msg|
  puts "Recv: #{msg}"
end
```

I think this method should be defined in `lib/hermann.rb`, that way that file can be:

```ruby
module Hermann
end

if Hermann.jruby?
 require 'hermann/java'
end
```

Which would make the extra class-level if statement on line 7 unnecessary