5.10.3 -- Fix main.css relative links in html pages

- The <link> tag was loading href="main.css", which gets a 404 when the
  page is in a subdirectory of the document root. The fix correctly adds
  .. path elements (parent directory) for each subdirectory level.

In other news, the "vendor" and "contrib" sections of this repository
now contain third-party code and resources, and hoplon libraries,
respectively. These are subprojects with their own project.clj files.