use {{ site.baseurl }} instead of {{ site.url }}

[doka]

Theme runs nicely on Github Pages if the site is setup as users or organizations pages, but links are broken if the site is a project page, see #215.

This PR is to correct this behavior by replacing {{ site.url }} by {{ site.baseurl }}.

See more info here.

[mmistakes]

This is an improper use of baseurl, see https://byparker.com/blog/2014/clearing-up-confusion-around-baseurl/

If you're going to use it both should be define eg. {{ site.url }}{{ site.baseurl }}

A better way to support url and baseurl is to do it similar to how I've done it in my other theme.

{% if site.url %}
  {% assign base_path = site.url | append: site.baseurl %}
{% else %}
  {% assign base_path = site.github.url %}
{% endif %}

Which is in an include and can be used as the variable {{ base_path }}.
Eg. <a href="{{ base_path }}{{ post.url }}">{{ post.title }}</a>

[sanmai]

What about relative_url and absolute_url?

{{ "/docs/assets/" | absolute_url }} => https://jekyllrb.com/myproject/docs/assets
{{ "/docs/assets/" | relative_url }} => /myproject/docs/assets

More info.

[mmistakes]

baseurl and url have been correctly used in the theme by relying on Jekyll's relative_url and absolute_url filters as @sanmai pointed out.

Currently in #265, and will land when merged.