Refactor link transforming

[teesloane]

• refactor: make site baseurl into it's own struct.
• construct links using the baseurl struct's "build" method.
• fix: files in a subfolder can now link to sibling files without resulting in a dead link.

if you have a file foo/bar/my_file.org and it has a link of file:another_file.org, before - this be a dead link, now, we grab the parent directories of the file that the link is found in and reconstruct the link so that file:another_file.org becomes :foo/bar/another_link.html.