Update vendored deps (except minio-go)

vendor/src/github.com/pkg/sftp/request-readme.md

@@ -0,0 +1,48 @@
+# Request Based SFTP API
+
+The request based API allows for custom backends in a way similar to the http
+package. In order to create a backend you need to implement 4 handler
+interfaces; one for reading, one for writing, one for misc commands and one for
+listing files. Each has 1 required method and in each case those methods take
+the Request as the only parameter and they each return something different.
+These 4 interfaces are enough to handle all the SFTP traffic in a simplified
+manner.
+
+The Request structure has 5 public fields which you will deal with.
+
+- Method (string) - string name of incoming call
+- Filepath (string) - path of file to act on
+- Attrs ([]byte) - byte string of file attribute data
+- Target (string) - target path for renames and sym-links
+
+Below are the methods and a brief description of what they need to do.
+
+### Fileread(*Request) (io.Reader, error)
+
+Handler for "Get" method and returns an io.Reader for the file which the server
+then sends to the client.
+
+### Filewrite(*Request) (io.Writer, error)
+
+Handler for "Put" method and returns an io.Writer for the file which the server
+then writes the uploaded file to.
+
+###    Filecmd(*Request) error
+
+Handles "SetStat", "Rename", "Rmdir", "Mkdir"  and "Symlink" methods. Makes the
+appropriate changes and returns nil for success or an filesystem like error
+(eg. os.ErrNotExist).
+
+### Fileinfo(*Request) ([]os.FileInfo, error)
+
+Handles "List", "Stat", "Readlink" methods. Gathers/creates FileInfo structs
+with the data on the files and returns in a list (list of 1 for Stat and
+Readlink).
+
+
+## TODO
+
+- Add support for API users to see trace/debugging info of what is going on
+inside SFTP server.
+- Consider adding support for SFTP file append only mode.
+