Use relative_url filter consistently and set baseurl to empty

[MarkusPiotrowski]

Follow-on PR, according to discussion on #180

Does seem to work, applied here: https://markuspiotrowski.github.io/

[peterjc]

Thank you!

[LalitNM]

@MarkusPiotrowski this needs to be done in some other places too, two of them are listed below, not sure if there are none other than these.

• https://github.com/biopython/biopython.github.io/blob/3e4d073472c89af3477137e92c423f44dd3a6caf/_includes/sidebar.html#L16

• https://github.com/biopython/biopython.github.io/blob/3e4d073472c89af3477137e92c423f44dd3a6caf/_layouts/wiki.html#L7

When I render this site on https://lalitnm.github.io/biopython.github.io (rather than https://lalitnm.github.io), these links do not work.

[MarkusPiotrowski]

@LalitNM Actually, I feared that there are possibly more places where this needs to be done... Do you want to give it a try?

[LalitNM]

Sure, but I might need your help...