Fix one bug and try to improve documentation

Hi,

First I really like what you did...
I like it so much that I want to use it for my Ansible scripts ;-)

Second, I have a small bug to submit (file ansigenome/scan.py)
I have also tried to improve a bit your documentation as you can see.

And finaaly, when doing ansigenome gendoc instead of ansigenome gendoc -f md the rst format does not seems to be well generated.

I also have a bug trying to genereate the graphviz graph:
ansigenome export 
you must supply -o <file> to write the png file
ansigenome export -o 'test.png'
  File "/workspace/users/albandri10/env/ansible/ansigenome/ansigenome/export.py", line 155, in graph_dot
    print graphviz_template
IOError: [Errno 32] Broken pipe

I have also find out that I have to add :
  authors:
    - name:  'Alban Andrieu'
      url: 'fr.linkedin.com/in/nabla/'
      email: 'alban.andrieu@free.fr'
      twitter: 'AlbanAndrieu'
      github: 'AlbanAndrieu'

In order to have Twitter or Github in the documentation.

There is no parameter in ~/.ansigenome.conf or doing ansigenome config

I am willing to help you to improve your tool. So do not hesitate to tell me if you need some help...
You will be my first contribution in python (I am learning it)

Best regards,

Alban