IOffset interface for different implementations.
Offset wrapper class and 32bit and 64bit implementations.
Fixed bit shift operations with 64 bit offset.
Test for consumer channel using both 64bit and 32bit offsets.
Disabled 64bit test on 32bit environment but other way round all tests are run.
Fixed new method setData in Offset.
Fixed new method setData in Offset.
Standard int offset constants instead of hexdecimals.
Added php-zookeeper installation apendix to readme.
Merge branch 'int64' of github.com:michal-harish/kafka-php

 - Code reviewd by Pau, and run php-cs-fixer to unify the code style of
   the library.
Fixed consumer script double wrapping of offset object.
Merged last changes from int64 branch, apparently the error come from the consumer script, not from the library.