title: Markdown-preview does't work in emacs markdown mode
body: <h3>Markdown preview command doesn't work.</h3>
  
  <p>I installed markdown-mode.el on emacs by using package-install.
  Then I created test.md file as a trial. Syntax hi-lighting apparently works fine in the text.</p>
  
  <p>When I used "C-c C-c p" command in order to show markdown preview, I got following error message in <strong>backtrace</strong> buffer. Even if I saved test.md file in current directory, it still said "No such file or directory". The file is located in "~/workspace/daily_log/test.md."</p>
  
  <p>I tried "M-x markdown-preview" instead of shortcut key. But it doesn't work,too.</p>
  
  <p>Do I make a mistake about usage of markdown-mode? Any help would be appreciated. Thanks in advance.</p>
  
  <h3>Error message in backtrace buffer</h3>
  
  <pre><code>Debugger entered--Lisp error: (file-error "Searching for program" "No such file or directory" "bash.exe")
  call-process-region(1 36 "bash.exe" "/tmp/emacsAxnXZ9" #&lt;buffer *markdown-output*&gt; nil "-c" "markdown")
  shell-command-on-region(1 36 "markdown" "*markdown-output*")
  markdown("*markdown-output*")
  markdown-preview()
  call-interactively(markdown-preview nil nil)
  command-execute(markdown-preview)
  </code></pre>
  
  <h3>my environment</h3>
  
  <p>OS: Ubuntu 14.10</p>
  
  <p>emacs: 24.4.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.12.2)</p>
  
  <p>markdown-mode: markdown-mode-20140914.1012/</p>