Add new utility functions to riak_core_util
Add new utility functions to riak_core_util

* `riak_core_util:compose/2`: Compose two functions.
* `riak_core_util:compose/1`: Compose all functions in the list.
* `riak_core_util:multi_keydelete`: Allow for deleting multiple elements
     from a list based on the provided keys. Using `multi_keydelete`
     avoids such silliness as the following:

```
List1 = lists:keydelete(...),
List2 = lists:keydelete(...),
List3 = lists:keydelete(...),
```

Kyorai/riak_core