Update references to new project location

* Change 'github/gollum' references to 'gollum/gollum'
Merge pull request #652 from simonista/update-references

Update references to new project location
Update README.md
Add basic support for symbolic links.
Merge pull request #658 from cpence/master

Basic support for symbolic links
Fix symlink base path, don't allow symlinks in bare repos.
Merge pull request #659 from cpence/master

Fix symlink base path, don't allow in bare repos