added Stuffit Support

The extraction tool can be found at
   -http://my.smithmicro.com/downloads/files/stuffit520.611linux-i386.tar.gz

src/binwalk/config/extract.conf

@@ -37,6 +37,7 @@
 ^lha:lha:lha ei '%e'
 ^iso 9660:iso:7z x '%e' -oiso-root
 ^microsoft cabinet archive:cab:cabextract '%e'
+^stuffit:sit:unstuff '%e'
 
 # Try unsquashfs first, or if not installed, sasquatch
 ^squashfs filesystem:squashfs:unsquashfs -d '%%squashfs-root%%' '%e'

src/binwalk/magic/compressed

 
 #------------------Compression Formats-----------------------------
+# Stuffit archives are the de facto standard of compression for Macintosh
+# # files obtained from most archives. (franklsm@tuns.ca)
+0   string      SIT!            StuffIt Archive (data)
+!:mime      application/x-stuffit
+!:apple     SIT!SIT!
+>2  string      x               : %s
+0   string      SITD            StuffIt Deluxe (data)
+>2  string      x               : %s
+0   string      Sef             StuffIt Deluxe Segment (data)
+>2  string      x               : %s
+
+# Newer StuffIt archives (grant@netbsd.org)
+0   string      StuffIt         StuffIt Archive
+!:mime      application/x-stuffit
+!:apple     SIT!SIT!
 
 # AFX compressed files (Wolfram Kleff)
 2    string        -afx         AFX compressed file data