Ensure website is cleared in the generate function

While commit c0425d5 addressed issue #6 by moving the content of
output-site into output-site/scipy-tutorial-2014 directory, it also
caused the publish script to push the content with the sub-folder.

This commit prevents this by ensuring the website is cleared before
each generation.
Merge branch '6-fix-styling-for-dexy-serve'

* 6-fix-styling-for-dexy-serve:
  Ensure website is cleared in the generate function