Paths to symlinks are resolved to their real path

[Axlefublr]

The call to std::fs::canonicalize makes it so it's possible to specify relative paths like ../somepath while not being in the repo root, for example.

The downside is that to make that happen, it needs to resolve symlinks (. and .. are hardlinks), so this includes any symlinks you might be providing the path to: you're going to get a link to the real file, rather than to the symlink (if the symlink points to something in the git repository, otherwise you're gonna get jumbled up garbage)

PRs are super welcome!