Fix README and docstring for options map in ssh/sftp

Fixes #15

Author: hugoduncan

README.md

@@ -101,8 +101,8 @@ SFTP is supported:
     (with-connection session
       (let [channel (ssh-sftp session)]
         (with-channel-connection channel
-          (sftp channel :cd "/remote/path")
-          (sftp channel :put "/some/file" "filename"))))))
+          (sftp channel {} :cd "/remote/path")
+          (sftp channel {} :put "/some/file" "filename"))))))
 ```
 
 SSH tunneling is also supported:

src/clj_ssh/ssh.clj

@@ -536,7 +536,7 @@ sh returns a map of
 (defn sftp
   "Execute SFTP commands.
 
-  sftp host-or-session cmd & options
+  sftp host-or-session options cmd & args
 
 cmd specifies a command to exec.  Valid commands are:
 :ls