The directory structure for viewing branches and code on Gitea / Gogs is
different from GitHub. This fixes that, so the Source Code link on the
gopkg webpage works, as well as the URLs to lines in the source code
included in GoDoc.

...instead of /go-{repo}/{repo}

This works better for us, as we have /writeas/go-writeas and
/snapas/go-snapas

Allows you to configure a different code hosting site besides
github.com, like one powered by Gitea or Gogs.

For details see:

https://github.com/go-fsnotify/fsnotify/issues/1

Besides enabling support for repositories with no master branch
defined, this will also make a bare "git clone" on a gopkg.in
repository create a local branch with the proper content and name.

Fixes #20.

Fixes #25.

See https://github.com/golang/gddo/pull/212 for the corresponding
change to godoc.org.

- Improve Repo methods and fields.
- Bring back documentation redirection on URL fragments.
- Fix hrefs in version map so they point to the SubPath
  and take OldFormat into account.

Add VersionList ([]Version) implementing sort.Interface.
Changed hackedRefs to also return a VersionList holding all valid versions for a repo.
Change Repo struct to hold parts and added methods to construct useful strings from those parts.
Comment out the whole nameHasversion() thingie. It was noted as obsolte made it harder to create clean Repo struct.

Caused a panic when repo could not be reached.

This reverts commit f4151cb744.