Improvements to proxiability

This commit introduces sensible prefix logic, and adds a Prefix field to
the gitPage type so as to link resources as <prefix>/res/<resource>.

Links still use gitPage.RootLink, but should start just using the prefix
plus the path. That will reduce the number of problems with http/https.

Closes #109
Remove ".." and "/" from root directory page

This commit also removes an accidentally included debug statement from
several commits ago and adjusts the directory page root link to obey
prefixes.

Closes #113