title: How make sympy.printing.latex use Newton's notation for time derivatives
body: <p>While in qtconsole, I can import <code>init_vprinting</code> from <code>sympy.physics.mechanics</code> and then use <code>dynamicsymbols</code> to acquire dotted derivatives. 
  But when I use <code>latex</code> printer, I get 'da/dt' instead. </p>
  
  <pre><code>a = dynamicsymbols('a')
  a.diff(t)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/VF0CX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VF0CX.png" alt="enter image description here"></a></p>
  
  <pre><code>In: latex(a.diff(t))
  Out: '\\frac{d}{d t} a{\\left (t \\right )}'
  </code></pre>
  
  <p>And I want something like</p>
  
  <pre><code>'\\dot{a}'
  </code></pre>