Define the same API as queue

[matrixise]

Currently, the API of erqueue has the get and put methods, but to be compatible with queue, we need to change and define a new API.

Current API

erqueue:put/2
erqueue:get/1

We need this new API

erqueue:in/2,
erqueue:in_r/2
erqueue:out/1
erqueue:out_r/2

[matrixise]

or maybe the API of Redis.