title: Both slashes and backslashes in URL generated by Bokeh show()
body: <p>I am using Holoviews(Bokeh) on Windows to create a scatter chart.
  When I want to show my chart in browser, I write</p>
  <pre><code>output_file('scatter.html')
  fig = hv.render(scatter)
  show(fig)
  </code></pre>
  <p>The file is created and saved on</p>
  <pre><code>D:/Docs/#Plots/Scatter/scatter.html
  </code></pre>
  <p>because my scatter.py is in D:\Docs#Plots\Scatter folder, and this is what I want and what I get. No problem. However show() tries to open in the browser the following page:</p>
  <pre><code>file:///D:/Docs/#Plots\Scatter\scatter.html
  </code></pre>
  <p>that is, show() generates an URL with mixed slashes and backslashes.
  Any idea how to fix that?</p>