Simple Distributed File System
We desined a SDFS which is tolerant up to two machine failures at a time. SDFS
is a flat file system with no concept of directions. 
The allowed file ops include: 
 1). put localfilename sdfsfilename
 2). get sdfsfilename localfilename(fetches to local dir)
 3). delete sdfsfilename 
 Our project is built thourgh maven. 
 To run our project in your computer, you should first change the predefined
 introducers in membership folder according to your own ip. And change the 
 original master in the LeaderElection.java according to your ips. 
 Then, you can use the command - mvn assembly:assembly to package our project 
 into an executeable jar file - mp3.jar. Then, use java -jar mp3.jar to run.
 Enter 'join' to join the system first
 After join in the sytem, you can choose the following action: 
 Enter 'membership' to modify the membership group
 Enter 'id' to show the membership id
 Enter 'leave' to leave the system
 Enter 'put localfilename sdfsfilename' to insert or update the file
 Enter 'get sdfsfilename localfilename' to get the file from the SDFS
 Enter 'delete sdfsfilename' to delete the file from the SDFS
 Enter 'ls sdfsfilename' to list all members storing this file
 Enter 'store sdfsfilename' to list all files storing in this member