title: Shiny Slider Input step by month
body: <p>I am writing a shiny and and wanted a slider for the date. The date in my data are monthly and I would like to step forward one month at a time. The <a href="http://shiny.rstudio.com/reference/shiny/latest/sliderInput.html" rel="noreferrer">docs</a> for the slider input say that the step value is either in second or days depending on the min/max parameter types. Currently I have:</p>
  
  <pre><code>sliderInput("slider", "Time", min=as.Date("2005-01-01"),
                                max=as.Date("2014-12-01"),
                                value=as.Date("2005-01-01"), step = 30,...)
  </code></pre>
  
  <p>I want to be able to step by month instead of by day but it doesn't seem possible from what they give me. Is there a snippet of js I could add that would give me this functionality? </p>
  
  <p>Clarification Note: I have read the docs for this function and to my best understanding there is no base functionality for this. The time format parameter, upon testing, only changes the labels not the values. I have seen a couple posts that access the values of certain widgets and was wondering if this was possible. Eg) </p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      $(document).ready(function() {
      var slider = $("#slider").slider();
   // override the default "nice" function.
      slider.nice = function(value) {
      var ref_date = new Date("2005-01-01");
   // each slider step is 1 day, translating to 24 * 3600 * 1000 milliseconds
      var slider_date = new Date(ref_date.getTime() + value * 24 * 3600 * 1000);
                            return [slider_date.getUTCFullYear(), 
                            slider_date.getUTCMonth() + 1, 
                            slider_date.getUTCDate()].join("-");
                            }
                            })
  </code></pre>