title: bokeh show zoomed-in plot from start
body: <p>Say I have data plotted for 50 years</p>
  
  <pre><code>import pandas as pd
  from bokeh.charts import TimeSeries
  df = pd.util.testing.makeTimeDataFrame(12500)
  p = TimeSeries(df, tools = 'xwheel_zoom,reset')
  </code></pre>
  
  <p>When I open the html file, it shows the whole data and then I can zoom in. Is there a way to specify that when I open the html file, it only shows say last year's data?</p>