Add a head block so people can easily extends the theme

[irevoire]

This would allow to extends the head parts of your theme easily.
Here is an example of index.html file we could put in templates/:

{% extends "sam/templates/index.html" %}
{% block head %}
        {{ super() }}
        <link rel="stylesheet" href="fenced_code_tab.css">
{% endblock head %}

[bellackn]

hey @irevoire, seems like this repo isn't actively maintained anymore. fyi, i've created a fork and merged your proposed change there - bellackn@e688bcb

[irevoire]

Nice!
Happy to hear it's useful for someone ahah