Connection pooling using the riakpool model

Some of the changes might not meet the coding guidelines/standards for Basho but the riak-erlang-client now has connection pooling using PoolBoy in a similar model to riak-pool.

This model allows the connection pooling to be bypassed entirely for those that don't need/want it.

The host/port can be configured in sys.config along with the number of connections to create.

```erlang
1> application:start(riakc).
2> pong = riakc:execute(fun(P) -> riakc_pb_socket:ping(P) end).
pong
3> 
```