Add configparser as requirement

Adding configparser as requirement

After a fresh install via pip I got this:  

```
mgaitan@traful:~/Documentos/slides/phasety+idtq$ hovercraft charla.rst html/
Traceback (most recent call last):
  File "/usr/local/bin/hovercraft", line 9, in <module>
    load_entry_point('hovercraft==1.1', 'console_scripts', 'hovercraft')()
  File "/usr/local/lib/python2.7/dist-packages/hovercraft/__init__.py", line 18, in main
    from hovercraft.generate import rst2html, copy_resource
  File "/usr/local/lib/python2.7/dist-packages/hovercraft/generate.py", line 8, in <module>
    from .template import CSS_RESOURCE
  File "/usr/local/lib/python2.7/dist-packages/hovercraft/template.py", line 2, in <module>
    import configparser
ImportError: No module named configparser
```
After install configparser it worked.