added feature count_value_key option.

you can also sum up specified key with count_value_key option.
for example, {"count": 321, "customer_id": 123 ... }.
INCRBY item_count:123 321.

<pattern>
  count_key_format item_count:%_{item_id}
  count_value_key count
</pattern>
fixed bug: In case that count_value_key's value is not Integer, automatic cast cause problem.
Merge branch 'feature/count_value_key_option' into develop
Update version
Merge branch 'develop'