Relative links

[cherylepatrick]

This relates to pull request #30

For a long time, we have used the jekyll relative_url filter to reference internal links (either to site pages or to stylesheets). For example, we link to a style sheet like this:
<link rel="stylesheet" href="{{ "/assets/main.css" | relative_url }}">
On my local machine, with snjekyll serve, this works fine. It also works fine on the live site supernemo-dbd.github.io/

Lately, it has NOT worked on my own GitHub pages site https://cherylepatrick.github.io/SuperNEMO-DBD.github.io/ . Without the changes in PR #30, that renders with no styling and with all the internal links broken - the reason being that they link to (e.g.) https://cherylepatrick.github.io/index.html rather than https://cherylepatrick.github.io/SuperNEMO-DBD.github.io/index.html

In PR #30 I fixed this by changing the links to something like
<link rel="stylesheet" href="{{ "./assets/main.css" }}">

That works on my local snjekyll setup, and on my GitHub pages. However it fails the Travis checks and @goliviero said that it didn't work for him on his copy (I'm not sure what he did differently from me). So I don't think we want to merge this PR as it stands, but I am not sure what we should do instead.

This is a known issue with GitHub pages but I haven't really seen any good suggestions of how to fix it so it works everywhere. Advice needed!