title: Converting m to km and string to float in pandas DataFrame
body: <p>I have this simplified DataFrame where I want to add a new column Distance_km.
  In this new column  all values should be in kilometres and converted to float dtype.</p>
  <pre><code>d = {'Point': ['a','b','c','d'], 'Distance': ['3km', '400m','1.1km','200m']}
  dist=pd.DataFrame(data=d)
  dist
      
    Point Distance
  0   a    3km
  1   b    400m
  2   c    1.1km
  3   d    200m
  
  Point       object
  Distance    object
  dtype: object
  </code></pre>
  <p>How can I get this output?</p>
  <pre><code>    Point   Distance    Distance_km
  0    a       3.8km          3.8
  1    b       400m           0.4
  2    c       1.1km          1.1
  3    d       200m           0.2
  
  Point           object
  Distance        object
  Distance_km    float64
  dtype: object
  </code></pre>
  <p>Thanks in advance!</p>