Xgit.Repository.put_ref/2 should support dereferencing tags.

[scouten]

• Add label: "TO DO"
• Add label: "good first issue" or "help wanted" if appropriate
• Add link to this issue in a comment near the TO DO comment

Describe What Is Incomplete
The function Xgit.Repository.put_ref/2 (and all implementations of this behaviour) should support derefencing tags and should have an option similar to --no-deref to suppress that behavior.

[scouten]

Updated to say that --no-deref is about unpeeling tag objects and not following sym refs. Removed 0.4.0 milestone for that reason.