v1.13.6

[GH-499] writeToSequential: improve tests for write errors
[GH-513] More context for EOF during client setup
[GH-516] RealPathFileLister: allow to return an error
[GH-525] Document the weirdness of the reversal of arguments to SSH_FXP_SYMLINK
[GH-526] request server: handle relative symlinks
[GH-528] Add support for working directory in Server
[GH-533] CI: add CIFuzz integration
[GH-537] Stop ReadFromWithConcurrency sending more data than it needs to
[GH-545] refactor sshfx encoding, fix link rot, go fmt
[GH-553] Marshal extended attribute data if FileInfo supports it
[GH-554] Properly handle io.EOF error conditions when reading