title: multiple api request using retrofit and rx java
body: <p>I am new to android and I have a scenario where I want to get get data from multiple api. Let suppose <strong>api_a</strong>, <strong>api_b</strong>, <strong>api_c</strong>, <strong>api_d</strong>. These api are independent of each other but I want to show data from these api in a mix Recycler View (<strong>horizontal and vertical</strong>). So I want to make these api call in such a manner so that I can get every api data at a time so that i can display in recycler view.
  I already using <strong>retrofit 2</strong> but for that I had to chain them one by one which is very lengthy and I think this is not a feasible approach. I know little bit about <strong>RX JAVA</strong> ,but I only know how to make one request at a time. Please help</p>