title: RxSwift emit starting value with time interval and modify it
body: <p>I need to decrease input value with every second, and print it. 
  When value reaches 0, then it becomes 100, and decreasing process repeats, and again.</p>
  
  <p><strong>For example:</strong></p>
  
  <pre><code>Given value: 
  -&gt; 234
  Timer starts decreasing with every second
   -&gt; 233
   -&gt; 232 
  ...
   -&gt; 1
   -&gt; 0 and the whole process repeats,
  
  but starts with value 100 
  (and again decreasing, reaches 0, starting from 100)
  </code></pre>
  
  <p>I know how to use timer in Rx, but how to connect it with described case?</p>