title: Converting from camelcase to _ in emacs
body: <p>Is there an emacs function to convert a camel-cased word to underscore?  Something, like:</p>
  
  <p><code>longVariableName</code></p>
  
  <p><code>M-x</code> <code>to-underscore</code></p>
  
  <p><code>long_variable_name</code></p>