Support smudge filter for git-crypt diff

When using git-crypt, the smudge filter is needed to see a diff of changed encrypted files. git-crypt adds the following to .git/config:

[filter "git-crypt"]
    smudge = git-crypt smudge
    clean = git-crypt clean
    required = true
[diff "git-crypt"]
    textconv = git-crypt diff

Please support the smudge filter so I can see diffs of encrypted files without having to go to git cli.

Thanks.