Simplify year output logic in post_index

[andreykurenkov]

While modifying the base theme to support tags and multiple categories, the year output on post_index got messed up multiple times due to it assuming all posts in site.posts will be posted on the post_index page (no if statements will be added or such). My post_index is modified in more different ways, but I think this particular change would benefit people forking the code in the future.

{% for post in site.posts %}  
    {% unless post.next %}
        <h3>{{ post.date | date: '%Y' }}</h3>
    {% else %}
        {% capture year %}{{ post.date | date: '%Y' }}{% endcapture %}
        {% capture nyear %}{{ post.next.date | date: '%Y' }}{% endcapture %}
        {% if year != nyear %}
            <h3>{{ post.date | date: '%Y' }}</h3>
        {% endif %}
    {% endunless %}

{% capture written_year %}'None'{% endcapture %}
{% for post in site.posts %}  
    {% capture year %}{{ post.date | date: '%Y' }}{% endcapture %}
    {% if year != written_year %}
        <h3>{{ post.date | date: '%Y' }}</h3>
    {% endif %}
    {% capture written_year %}{{ year }}{% endcapture %}

[mmistakes]

Thanks!